Question Of The Week

106 Hand-Calculated MPG Confessions

We asked our readership if they, “Trust the Dash, or Do the Math” to calculate their truck camper rig miles per gallon.  Over one-hundred readers answered, most with a resounding “Do the Math”.  A few said, “Who cares?  I just want to go truck camping, and have fun!”

We’re in both camps now.  We hand-calculate, but will keep on truck camping no matter what the results.  Besides, you can’t put a 5,000 pound truck camper on a Prius, at least not for very long.

“Why does it matter?  You already own the truck and camper.  It burns what it burns.  There’s not really a whole lot you can do about it except slow down a little.  I say, just forget about what mileage you get and enjoy the trip.  If you feel like it burns too much fuel, sell the rig and find something more economical.  Worrying about a constant is only going to upset you at how low it really is.” – Brian Rushing, 2014 Ram 3500 diesel, 2013 Lance 855

“We have a log book in the truck where we keep every fuel purchase.  We notate the gallons, price, and miles on every tank, calculating by hand the mileage on each tank.  At the end of the trip we have an overall average to see.  It is interesting to see how the terrain, speed, and especially the wind affect the miles per gallon.  We get between eleven and twelve plus mpg at 65 mph speed.” – Dewey Lackey, 2003 Silverado 3500HD diesel, 2014 Lance 1172

“I hand calculate my fuel mileage using a calculator and recording at each fill up.  At the end of a trip, I divide the total miles driven by the total fuel used always starting with a full tank and ending with a full tank.  I do have an onboard computer as part of some Banks aftermarket equipment I installed and find that it is very accurate, but I still hand calculate.

After driving almost 12,000 miles on a trip to Alaska this summer, I averaged 12.49 mpg overall and the Banks onboard computer showed 12.5.  From tank to tank, the onboard computer seems to be off as much as .2 mpg +/-.” – Eldon Rhodes, 2008 Chevy 3500 HD, 2011 Lance 1050

“I hand calculate and it’s about 10 percent off all the time from the dashboard.  We pretty much have the same truck as TCM, except I have 4.10 gears and it stays in MDS (cylinder deactivation) a little longer due to less effort due to torque multiplication when loaded.  Loaded I average about 12 mpg hand calculated and unloaded about 18 mpg hand calculated.  The display says 13 and 20 on average.” – Roy Del Pozo, 2014 Ram 3500 gas, 2013 CampLite 8.6

“I never trust the dashboard fuel mileage other than the current estimate.  I use an application called Gas Cubby to track all vehicle expenses and mileage calculations.” – Timothy VonWolffradt, 2014 Ford F350, 2011 Lance 850

“Rule number 1: Don’t believe the lie-o-meter.  That said, I’ve found mine is actually relatively accurate over the long haul.  For example, loaded with camper and boat in tow running 1,700 miles to the Florida Keys, I found that my dash readout was pretty accurate based mostly on the DTE and what I was seeing on the odometer, per tankful.  At 35 gallons and 12 mpg that’s 420 miles on a tankful.  Resetting the ODO, I was easily seeing in the mid to mid-upper 300s before pulling off for a refuel, dumping in 26 to 28 gallons.  So, 420 miles was definitely in the mix, which would indicate 12 mpg.  And that’s a 3,600 pound camper wet and 4,000 pound boat and trailer in tow.  Without the boat in 2011, on the way home, my dash was reading almost 14 mpg.” – Nik Rende, 2011 Ram 3500, 2005 Lance 1010

“I check by hand.  I use a Scan Gauge to watch mileage.  It is accurate.  Driving by the Scan Gauge really helps keep the mileage up.” – Bill Harr, 2005 Toyota Tundra, 2013 Four Wheel Camper Hawk

“I hand calculate the fuel mileage.  I don’t have the computer to do it for me.  I use the phone calculator.  The truck mostly gets 10 mpg, so I can pretty much figure it in my head.  If it looks different, I’ll use the calculator.” – Jeff Hagberg, 2002 Ford F250 SD, 2006 Travel Lite 800SBX

“I run a pen and paper continuous mileage log on all truck expenses, maintenance, and fuel.  I occasionally do hand calculations after a number of fill-ups to even out spot variations and to compare to the dashboard numbers, which optimistically tend to run a little over 10% high.  I still find the dash numbers useful as a trend guide, like if I do an extended run at say 63 mph versus 71 – do I see a mpg improvement, and how much?  Or, if I adjust my Smarty from 99% down to 93%?” – Wil Painter, 2007 Dodge diesel, 2010 Host Cascade

“The dash board results on our truck is usually very, very close to hand calculations.  We’ve had this truck since new in December of 2003.  Loaded with the camper and everything, it gets 15 mpg.  I just had a check engine light issue related to transmission electric supply.  I don’t know if they reset any computers to different settings or not.  Our upcoming three week trip next week will tell the tale.  Funny though is that the truck ran and shifted just fine while the issue was ongoing before we were able to get it fixed.  Thankfully, it was only a $200 one day fix!” – Cheryl Nelson, 2004 Chevy 3500 diesel, 1990 Shadow Cruiser 9.5

“Whenever we buy a car or pickup, we test various grades of fuel to find the best cost to milage ratio.  Hand calculation only!” – Philip Tron, 2009 Chevy 3500, 2012 Lance 1050

“I calculate the MPG by resetting the trip miles each fill-up and dividing that number by the fill up gallons.  With or with out the camper, I get between 10 and 12 mpg depending on whether we’re doing stop-and-go city driving or 59 mph, 2,000 rpm, cruise control across the central plains of Nebraska.  My miles per gallon are accurate, but the tenths are off on what the dashboard says.” – Jesse Taylor, 2005 GMC Sierra 2500HD gas, 2006 Lance 815

“I’ve done it doth ways but, since the dashboard data agrees with hand calculations within 1%, there’s no reason to do the math by hand.  Mileage with the camper varies quite a bit depending on how fast we drive.  We get right at 13.5 mpg at 65 mph, dropping to around 11 mpg at 70 mph, and a little under 10 mpg at 75 mph.  A  little extra speed really costs.” – Phil Rodacy, 2012 GMC 3500 diesel, 2006 Okanagan 90W

“I have cross checked on my F350 and have found it to be very accurate.  Lots of things can affect mpg calculations such as a different tire size from OEM and over/under inflation pressures.  These can throw the computer off and, if you drive a diesel with longer distances between fill ups, the effect becomes accumulated +/- in the on board computer.” – Pryor Donald, 2011 F350, 2009 Arctic Fox 1150

“The actual mileage we experience is about 10% lower than the amount computed by the truck.  On our recent 15,000 mile trip around the US and Canada, the truck said that we averaged around 12 mpg.  In reality we got a bit over 10 mpg.  Since putting in the 56-gallon fuel tank, we noticed that the gallons used indicator is off by the same 10%.  I conclude that the fuel flow sensor is not reporting the correct fuel flow.  Maybe it’s mis-calibrated, or by design?  The cynic in me leans toward the latter.” – Jim Goodrich, 2006 Chevy Silverado 3500 diesel, 2008 Lance 1191

“Depending on wind direction and speed, versus ideal conditions with no wind, I get eleven to the high twelves.  Hand calculated seems to always agree with my dash data.  I simply divide total miles by gallons pumped.” – Dennis Glow, 2003 Ford F350 gas, 2014 Travel Lite

“My wife, Cheryl, has kept track of all of our truck camper trips using pen and paper.  With over 13,000 miles, we have averaged 14 miles to the gallon.  As soon as I noticed that we put in at least one more gallon than the truck said we used, I quit believing the dash numbers.” – Matt Reinker, 2006 Chevy 1500 gas, 2007 Northstar TC650

“I hand calculate every time I fill up.  I keep a little notebook handy and enter the miles traveled and mpg and then add a brief note on what the majority of driving has been on the tank of fuel (city or highway or combo).  I have two years of data.  What I do is fill up immediately before I load the camper and immediately after so I can see how the camper affects the mpg.  What I found is that the truck averages 15.5 mpg without the camper and 11.5 with the camper.  The truck communicates the average mpg to my smartphone app and shows 14 mpg.  That is only the total in the history of the truck so it is a little meaningless.” – David Miller, 2012 GMC 2500HD gas, 2012 Travel Lite 890SBRX

“We always calculate our mileage with a calculator or iPhone app.  The dashboard computer is ridiculous, showing that our mileage is from 2 to 6 mpg more than our true mileage!

We also have a ScanGauge in our truck that plugs into the vehicle’s computer diagnostic port and mounts somewhere on the dash.  This device can be programmed to show dozens of engine readouts, with four visible on the screen at one time.  I have ours programmed to show RPMs, average mpg, current mpg and gallons per hour.  It is a great monitoring device and can also be used to check for trouble codes, or codes pending.  Unfortunately, it always shows that our mileage is three mpg less than our actual mileage.

Personally, based on my experience, I don’t trust any dashboard device as being accurate, especially after a friend with a truck identical to ours insists that he gets 36 mpg because his dashboard computer shows that reading.  This would give him a range of over 1,300 miles on one tank!  That would be nice!

On a month-long trip last Spring, we averaged 15.7 mpg driving at 60-62 mph at about 1,700-1,750 RPMs with a light foot on the accelerator.  This was mostly flat driving with only a few mountains to negotiate through Virginia and West Virginia.  Our overall mileage, non-towing, for the two years that we have had our pop-up Northstar is 14.9 mpg.

When towing either our boat, a C-Dory 22, or our UTV on a trailer with a canoe on top, our mileage drops from an average of 13.2.” – Nick Rukavina, 2006 Dodge Ram 3500 Cummins diesel, 2012 Noorthstar TC650

“I do it by hand and get 9-9.5 mpg to 10-11.5 mpg, and sometimes as much as 12 mpg.” – Jesse Black, 2012 Chevy 3500 HD gas, gross weight 12,440 pounds, 2009 Lance 1055

“We love our truck.  It’s just about perfect, and never gave us any real problems.  Then again, the overhead mpg indicator is so far off it’s comical.  It reads 30 mpg around town and 20 to 22mpg highway loaded, while hand calculations indicate 12 loaded.” – Bill Kichman, 2006 Dodge Ram 3500 diesel, 2005 Lance 881

“I hand calculate and record all fuel purchases.  Empty I get 19 to 21 mpg at 60 mph.  With the enclosed trailer, loaded at 7,000 pounds, I get 13 to 14 mpg at 60 mph.” – Mark Harrison, 2005 Dodge 2500 diesel, still in the market for a camper

“Most of our recent travels are between Georgia and Colorado for the summer.  Thus we experience all types of driving conditions.  In all cases when traveling to the western states, we will be towing our Jeep Wrangler Unlimited. 

 Since I have owned the truck since new, the displayed mileage has never been correct.  It does not make any difference if there is a load or not.  Loaded the “intelligent device” will register between 11.5 and 13 miles per gallon.  The old fashioned pencil and paper method is generally 2 mpg less.

My issue – why are the manufacturers installing these “high tech” devices which are mis-leading and not accurate?” – Warne Todd, 2000 Ford F250 diesel, 2005 Lance 981

“I wouldn’t say we trust our dashboard fuel mileage display, but we don’t hand calculate it either (we just fill up well before we get to a quarter of a tank).  Our computer says we are getting about 9.5 to 11.3 miles per gallon with the camper on, and about 12.5 to 13.3 with it off and in traffic.  We certainly didn’t buy the truck for the fuel mileage, but rather for the towing and hauling capacity.

We have hand calculated on one trip (last August, when we were also hand calculating for our recently supercharged Miata that we were having to drive separately for 6 hours since it wouldn’t fit on our current trailer).  The truck oscillated from dead-on to 3% off, which we feel good about, especially after reading the numbers on the Dodge.  We were more excited that our Miata, now with 260 hp, got a computer and hand-calculated average of 55 mpg from Denver to Grand Junction, and 48.8 on the way home during a huge flooding rainstorm!  Average that with the truck and we have a pretty good fleet rating, almost meeting the CAFE standards!  I guess if we can find a way to get the Miata to carry the truck camper and tow the RZR, we can then start to worry more about gas mileage.” – Tracy and Steve Schuster, 2012 Chevy Silverado 3500 diesel, 2012 Lance 992

“I do both.  I have a commercial fuel account that asks for mileage on fill up.  With the monthly statement mpg is calculated.  I find the dash mpg is pretty accurate.  I get around 10 to 11 mpg with the camper and 12 to 14 mpg unloaded with the shell on.” – Bob Holland, 2012 Dodge 3500 diesel, 2013 Adventurer

“I learned a long time ago that my dashboard mpg is consistently inaccurate.  I have also heard the same from other Dodge Ram 2500 owners.  It is between 10 and 15 percent wrong, which is too high.  This was with stock tires and both loaded and unloaded.  Now that I have oversized tires, I pay no attention to the computer’s estimated mileage.  I reset my trip odometer at every fill up and then calculate manually.” – Mike V., 2006 Dodge Ram 2500 diesel, Northstar Laredo SC

“I do hand calculation with miles from the odometer.  I averaged about 13 mpg on a trip to Newfoundland recently.  The dash board is fairly accurate.” – Ronald Day, 2008 Chevy Silverado 2500HD diesel, 2005 Sunlite 865SB

“I hand calculate my mileage with pen and paper.  I don’t know how it compares with my dashboard data.” – Edwin Groenendyk, 2008 Chevrolet Silverado 2500HD gas, 2010 Palomino Bronco 1251

“When I first bought the truck used, I was so excited driving home from Paducah, Kentucky,  getting 27 mpg.  Then I started hand calculating and the mpg went to 19 for highway and around 16 for city.  When we put camper on the mpg is anywhere from 13 to 15.5 mpg.

After about a year of driving the truck, I had mileage checked on a marked course and it was determined that my speedometer was off by 4%.  So, when I hand-calculate, I add four miles for every hundred miles I have driven, and then calculate.” – Ed Krech, 2006 Dodge 3500 diesel, 2011 Northern Lite 8-11

“I always hand-calculate our gas mileage on all our vehicles.  Any new or new-to-us vehicle has a note pad and pencil in it and mileage is calculated for about six months on each fill up.

We also clear the trip mileage at each fill up.  I always do an in-my-head rough calculation at each fill up.  It tells me if there is a problem or not.  Our Dodge new got the mileage on the window sticker, and sill does.  I get 20 on the highway and 11 in town empty.  I get 10 hauling our trailer and 12 to 15 with camper on, and hauling a tow vehicle.  I get 15 with just the camper on.  Why would I trust a manufacturer when we know they lie and will do anything to avoid a recall?” – Sal, 2008 Dodge Ram 1500 gas, 1994 Northstar pop-up

“I have never really calculated my fuel mileage.  It burns what it burns.  As long as the engine is running smoothly, has the power and torque, and doesn’t smoke, I am a happy camper.  I look at it this way.  I’m having fun doing what I am doing and if it costs me a few more bucks on one trip than the other for fuel, so what, who cares?

There are so many variables to consider – load, road conditions, terrain, head or tail winds, outside temperature, idling time, if I stay in lower gears too long, and the speed I am driving.  Other factors are gear ratios, wheel and tire size, and whether it’s a two wheel drive or four wheel drive vehicle.

Fuel economy is not going to be the same for each trip even on the same route unless all the factors are exactly the same.  I know by the sound, power, and the smoothness whether my engine is running at top efficiency.  If everything is running well, I am happy.  I don’t watch a mileage meter or sweat the small stuff like putting a few extra liters of fuel in the tank at the next stop or spend time doing the math to see what I burned and try to figure out why.  And we pay more for fuel in Canada.” – Grant Smith, 1998 Dodge Ram 3500 diesel, 2012 Bigfoot 1500

“We have hand calculated every single tank full on this truck and camper combination and recorded every fill up with details in our truck log book.  We did the same with our 2000 Ford F-350 V-10 Gasser.  For twelve years, overall average for that truck with the camper was 11.8 mpg.  We use a calculator that is kept with our logbook in the truck.

We just completed a nearly 5,000 mile journey this Fall.  With the camper loaded, overall average ran 14.5 mpg.  The 2012 Ford info display is almost always within .1 or .2 mpg at fill up.  The actual gallons used is always quite close as well.  I try to fill the tank to the same on spot on the fuel filler neck every time.” – Gary Gadwa, 2012 Ford F350 diesel, 2011 Eagle Cap 950

“I calculate my millage using an iPhone app called Road Trip that keeps all my maintenance records for all my vehicles along with plotting my mileage and expenses, both short term and long term.  My truck doesn’t have a mileage computer but I would not trust it if it did.” – Jeb NY, 2000 Ford F250 diesel, 2005 Shadow Cruiser pop-up

“I calculate with a hand held calculator; miles divided by gallons, which equals mpg.  It is very accurate compared to the dash readout, but my truck only has 3,500 miles on it.  Empty I’m getting 16 to 18 mpg at 65 mph.  Loaded I’m getting 14 mpg.” – Paul Roberson, 2014 Ford F350 diesel, 1988 Lance 930

“I have a dually crew cab with a 454 7.1 litre motor with a 10,000 pound vehicle weight, a 4,000 pound camper, and a 1,500 pound Bayliner in tow.  We stop for a pit stop every two hundred miles and top it off.  Gas mileage; irrelevant!” – Joe Gosselin, 1996 Chevy, 2007 Lance 1181

“I calculate fuel economy for every fuel fill-up.  I use the Fuelly App exclusively to track my fuel consumption and fuel economy.  It allows me to see the difference between city and highway, with and without loads or camper, and even pulling our fifth wheel.  My diesel Ram 3500HD gets significant mileage differences, pulling and hauling.  For instance hauling the truck camper it got 13 in the Rocky Mountains and 16.5 on the I-40 highway at 60 mph.” – Jim Comperchio, 2013 Ram 3500HD diesel, 2015 Northstar 850SC

“My previous 2000 Ram 2500 dashboard was nearly 100% accurate.  My 2008 dashboard is 15 to 20% too high.  I have a Prius and its dashboard is about 7% too high.  I use GasCubby to track my mileage for comparison to the dashboard.  I’ve only had the camper for a month.  Bringing it up from San Diego I got 14.7 mpg.  I filled up just before I started and again after I arrived to get the mpg.” – Pete Haidinyak, 2008 Ram 3500 diesel, 2014 Lance 1172

“I’ve been trusting the dashboard computer, but your article has me wondering if I should verify it by hand.” – Ken Woodward, 2012 Ford F150 gas, 1994 Trav-L-Mate 8’

“I have a calculator on my phone, so I do not use an app.  The truck usually shows 12.5 or 13 mpg, and it’s usually lower by a mile or mile and a half.  Both could be better but I like using the power that I have.  Doing 75mph on the road is not unusual for me, even with a trailer.” – Alfonse Pinkus, 2007 Ford F350 diesel, 2013 Hallmark Cuchara

“I have done the math with pen and paper since the truck was new.  I was so surprised. The dash display is always within a couple of tenths of the hand-calculated mpg.” – C R, 2012 Chevy Silverado 3500HD diesel, 2011 Carriage Cameo 35SB3

“I do a simple hand calculation on each trip.  Depending on my driving, and the road grade, I average 14.5 to 15 mpg.  My slow speed is typically 70mph.  I typically run around 75, and sometimes close to 80 mph.

If I slow down I can get 15.5 to 16 mpg with camper on and 20mpg with camper off.  I rarely slow down.” – David Carvalho, 2006 Ram 3500 diesel, 2013 Alaskan cabover

“Haven’t you ever been lied to?  If you are going to rely on others or other things, you’re in for a big surprise.” – David Weinstein, 1999 Ram 3500 diesel, 2005 Arctic Fox 1150

“When I’m curious, I will calculate my fuel mileage by hand.  In the end, it is not going to make any difference what it is.  I’m happy to get out of the house and whatever gas it takes is the cost of that happiness.  If I was misled by an automotive manufacturer from what was posted on the big window stickers when I bought a new vehicle, then I might be disappointed.  But I have learned not to put all my faith solely on tech gadgets like a GPS or a handy dandy on-board fuel mileage computer read out.  I still carry a cell phone, emergency supplies, and a yes, a good old map.  How many times have you gotten lost using your GPS?  Full up that bid ol’ gas tank and hit the road and don’t look back.  Have fun and enjoy the journey.” – Stan Kennedy, 2005 Toyota Tundra, Access Cab, Four Wheel pop-up camper

“That is why the dash board data is nicknamed, “The Lie-O-Meter”.  The only true way is hand calculating, but with diesel, you need to do this over several tanks.  As some fill faster than others, causing foaming.” – Frank Mertes, 2006 Dodge 3500, diesel, 2007 Sunlite 955SD

“I have a spreadsheet that all gas purchase are entered into.  At 5% off, our Ford seems to be much closer than yours, but indicates worse rather than better mileage.  Loaded we are over 15,000 with camper, tandem cargo trailer, the Harley, and all our stuff.  We got 24.5 l/100km average (11.5 mpg imperial gallon) on recent 15,000 km trip across Canada.” – Paul Kroeker, 2008 Ford F350 gas, 2008 Okanagan 85SL

“I always have hand-calculated mileage.  In each vehicle I own I have a notebook where I write down the data at each fill up.  I later transfer the information into an Excel spreadsheet where I track mileage, graph mileage, keep maintenance records, and track part numbers, etc.  So, it is easy to re-order the proper parts as needed.  I am old fashioned and don’t trust entirely any data from the auto makers gauges, as it is easy to discover errors or variations from reality.  Ever drive past one of those digital speed readouts and compare it to the speedometer?

I must say I was surprised when you had to post the mea culpa about trusting the dash readout.  I thought everyone knew those things as lie-o-meters, or at least understood that they used algorithms that couldn’t possibly match the end result that one would get at a fill up?  Some vehicles show instantaneous mileage, some show an estimated average mileage, some allow you to switch between the calculation types.  As you burn through a tank, the estimated average mileage should probably get closer to the actual outcome, and be less influenced by the current driving conditions.

I like the algorithm they programmed into my Kia car, as it rarely is optimistic and is generally within about 3-5% of the hand-calculated result.  I agree that the variation you experience on your truck is greater than one would expect with modern electronics.” – David Schmitt, 2007 Ford F350 diesel, 2014 Four Wheel Camper Grandby

“Neither.  I note the dashboard data for relative consideration and to mentally forecast my next fueling location.  In the old days, I’d hand-calculate and even keep a log book, but why bother?  I have what I have, so to go where I want to go, I pay the going rate.  Speed and foot pressure seem to have the biggest effect.  The lowest mpg has been about 9.5 (guesstimate) versus 14 or so when I’m just loafing along.  I think I possibly could do better, but, as I said before…” – Mark Obert, 1999 Ford F250 diesel, 1999 Lance 920

“At first I was trusting the dash, but one day I decided to do the math.  What a shock the difference was.  I recently had new injectors put in the truck at the dealer.  When I got the truck back, I first noticed it ran much better than it ever did.  The mileage did go down a minor amount.  I have had this truck since 2009 and it only had 17,000 miles on it when I bought it.  Now, I have checked the mileage via the dashboard and paper and pen.  There is only 10ths of a mile difference now.  So there must have been some serious re-programming involved.” – Ron Ewald, 2003 Chevrolet 2500HD diesel, 1995 Weekender by Skyline 11 Footer

“Hand-calculated.  I simply use my hand calculator at most stops.  I learned years ago that the various built in mpg computers were inaccurate.  Even on late model vehicles they are notoriously over optimistic.  When loaded down I average about 9.5 mpg. However, I leave my dog inside with the air conditioning running whenever I stop and I go over the CAT scales at around 13,450 pounds, so I’m pretty heavy.” – David MacArthur, 2008 Ford F350 diesel, 2011 Lance 992

“We do the math!  Probably it’s just habit from the old days.” – Jeannie Coushaine, 2001 Ford F350 diesel, 2012 Chalet DS116RB

“I neither trust the dash board fuel mileage, nor the odometer.  I hand calculate and use the GPS for true mileage.  I have found either the speedometer/odometer is almost always off, or the tire diameters (wear, brands, inflation, etc.) is incorrect on every vehicle I have owned – Ford, GM, Toyota, Suzuki, Subaru, and on and on.” – Philip, 2012 Ford F-350 gas, 1994 Lance Squire Lite 150

“When I check it by hand calculating miles driven divided by gallons purchased I get 11.5 to 13 mpg.  I don’t have any idea of the accuracy of driver info center calculations.” – James Burns, 2005 GMC Sierra diesel, 2008 Eagle Cap 850

“I occasionally verify by calculation, but the DIC has always been accurate, so I don’t worry much about it.” – Bill Tex, 2006 Chevy diesel, 2013 Eagle Cap 850

“I get around 12 mpg.  I use the dashboard average.  I do reset this every time I am hauling the camper.  I found that if I don’t reset the mpg gauge than I get off readings.  I have checked this by the hand method, less camper, so I believe it is accurate because it is has been close many times.” – Steve Evans, 2011 Ram 1500, 2012 Lance 825

“I have a 2005 Ford F-350 diesel, dual rear wheel, crew cab, four wheel drive, automatic with 4.10 gears. The camper is 2013 Arctic Fox 996 and we pull a 12’ Doolittle box trailer.  Loaded with everything we take along to stay two to three weeks at a time, we gross out at 19,300 pounds.  We are about 40 feet long.  I know that’s more than we should be at, but believe me with everything we did to the truck, it handles the load and does just fine.

We hand-calculate the miles with every truck we have and the on board computer has been way off.  If I trusted those, I would be sitting out on a mountain some where out of fuel.

The computer says I get 22 mpg.  With pen and paper I say we get 9.5 which is good.  If I have just the 996 and no trailer, I get 11 mpg if I keep the speed about 65 mph.  Even with the trailer and running about 70 to 75 mph I have never gotten below 9 mpg.” – Barry Anderson, 2005 Ford F-350, diesel, 2013 Arctic Fox 996

“I hand calculate mpg using my phone’s calculator.  My hubby, however, guesstimates by the fuel gauge, resulting in him thinking we get much better mileage.” – Lois Zell, 2005 Ford F350, 2009 Lance 1040

“On our trip to New England, we averaged 14.5 to 15 mpg going, and about the same coming home.  I normally average unloaded 18 to 18.5 mpg.  I was going by the readings on my truck.” – Tim Chapell, 2013 Ford F150, gas, 2013 Palomino 1251

“I record the date, mileage, gallons, trip odometer, computer average mpg, and cost at every fill-up.  Typically, I will take what the computer average mpg states for the last tank full.  If I do the hand calculation for that tank fill-up, it may vary by up to 0.6 mpg of the average the computer states.  However, if I take a larger sampling, say ten or more tank fills versus fuel use, and average that information, it typically agrees with the average of the computer mpg numbers for those tank fill-ups within less then 0.1 mpg (that is less than one tenth of a mile per gallon).

I would say that is acceptable.  With the camper on the truck and driving at around 60 to 65 miles per hour, my mileage can vary from about 12.5 to 14.5 miles per gallon.  With no camper, my mileage varies 17.5 to 19.5 depending on the mix of local to highway miles.  The truck as factory equipped, without the camper, weighs 8,000 pounds.” – Jeff Baker, 2011 Ford F250 diesel, 2012 Lance 855S

“The anguish from the mpg number on the dash board is similar to the anguish you receive at Christmas time when you open a large box expecting a toy only to find it contains clothing.  There is nothing you can do about it, but grin and bear it. 

You can travel with less fresh water, plead with the wife to bring less clothes and shoes.  She might plead not to bring so much liquid refreshments, but that mpg number is still there. 

This summer we did a 11,000 mile trip to Alaska and never once did I look at the mpg.  Whether we were able to do 8 miles or 12 mile per gallon, the distance between cities did not change and we were still going there.” – Ray Fair, 2013 Chevy Silverado 2500 gas, 2012 Lance 825

“My wife and I have hand-calculated our fuel mileage on every vehicle we’ve owned for the last 48 years.  We keep a log book in the glove compartment in which we note the date, mileage, number of gallons purchased, per gallon price, and miles since the last fill-up.  We also record any maintenance in the log along with the mileage.

Most of the entries can be completed while fuel is being pumped, and it takes only a few seconds to fill in the remaining information.  Mileage can be calculated right away or later using a pocket calculator.

We average about 13 mpg, driving at 1,500 rpm at about 63 mph.  We never check the dash mileage unless we’re pulling a trailer.  We got a Transfer Flow replacement 50 gallon tank for extra range.” – Thomas Wilson, 2012 Ford F250 diesel, 2013 Outback Apex 8

“My GMC is about 7% high in its estimate of mpg.  I refer to it as “Chamber of Commerce information” and do my own calculations based on odometer and fuel purchases.  A lot of friends use the info from the on board computer.  I challenge them to do the calculations.  They are all wrong if they don’t.” – Dwight Olson, 2012 GMC 2500HD diesel, 2005 Airstream 31′ (pardon me – I think I am referred to as a “lurker”)

“Hand-calculate.  We record every fuel purchase in a notebook, and then calculate the true mileage in a spreadsheet.  The dash shows 11 to 12+ mpg, and the spreadsheet shows 9.6 to 11 mpg.  Funny, we tried a diesel performance module and the dash showed we were getting 13-14 mpg!  When we hand calculated our average was still around 10 mpg.” – Don Graf, 2008 Ford F350 diesel, 2013 Arctic Fox 865

“I never trust what the computer tells me.  I always write the distance traveled on the gas receipt and use an Excel spreadsheet to do the math.  It always differs by a little and/or a lot.

It depends on if you take the time to fill the tank to the brim or if you simply stop it when the nozzle quits.  If I fill it to the brim, I can sometimes get well over a gallon of more gas in tank, which would drive down the mileage.  If I quit when the nozzle stops, then I will get higher miles per gallon.  The trick is to be consistent on how you fill the tank.

I also do this with my car.  What the car computer mileage says and what the hand calculated says is always different.  In all cases, it is lower than what the truck and/or car computer tells me.  So my advice is to always hand-calculate if you want to know the real mileage.” – Mark Turnbull, 2013 Chevy 3500HD gas, 2011 Four Wheel Camper Hawk

“I have hand-calculated mpg for years with all of my vehicles.  On those with dash mileage indicators, I have always found the dash reading to be a two to three mpg higher than actual, even on my Prius.

There are several reasons for this.  One, there is no fuel flow meter.  All dashes use the engine computer data including speed and then calculate the mpg.  I find them most accurate if you can maintain steady speed on flat roads with no wind which isn’t possible in many places.

The truck and camper gets anywhere from 12 to 15 mpg depending on speed and headwinds.” – Don Berg, 2008 Chevrolet 2500 diesel, 2007 Pastime 8′

“I have checked my mpg by hand with a calculator and pen and paper against my electronically calculated mpg and surprisingly the numbers came out very close, within a half mile per gallon.  So, I’ll just depend on the dashboard from here on out.  The best on my Ram was 20.2 mpg and the worst was 15.5 mpg.  On a long trip, using cruise control, more than 20 mpg is easy to achieve.  Once I’m off the highway, and getting into the 8 gears, it drops pretty fast.  But you gotta love this truck regardless!” – Dan Daddieco, 2014 Ram 1500 gas, No camper for this truck, too under-equipped

“My electronic readout is very close to actual mileage.  I get between 12 and 13 mpg with the Lance truck camper.  When the dash tells me I averaged 12 mpg, my actual is usually 11.8.  It is so close I rarely hand-calculate any more.  I would get better mileage if I didn’t have a 4:10 rear axle, but I need the 4:10 because I also use the truck to tow a 15,000 pound fifth wheel.” – Ron Moeller, 2014 Ram 3500 diesel, 2012 Lance 850

“Honestly, I just trust the dashboard computer.  Maybe I shouldn’t, but I do think given changing road conditions that it seems to make sense.” – Al Stebbins, 2006 GMC 2500 HD, 2005 Northern Lite 8-11Q

“I hand-calculate mpg.  I keep a log that includes where the fuel was purchased, cost to fill up, number of gallons purchased, odometer reading, and mpg that the truck’s computer calculates.  I then periodically enter this information into a spreadsheet that calculates cost per gallon and actual mpg on each fill up.  I also calculate mileage on road trips with and with out the camper and with and without towing the Jeep.  I’ve found the truck computed mileage to be very accurate, usually somewhat optimistic, but seldom off by more than three-tenths of a gallon.

At last check, the my hand-calculated mileage for 30,175.8 miles is 15.58 mpg.  I average about 17.6 mpg on the open road without the camper and 13 mpg with the camper.  These are hand-computed numbers.  I tend to fill up before I use half of the 38 gallon tank.  I’ve noticed the closer I get to empty before filling up the more accurate the truck computed mileage is.” – Dave Erickson, 2011 Ford F350 diesel, 2006 Arctic Fox 990

“None of the vehicles I’m familiar with have accurate fuel mileage readouts, including the Dodge.  I do a rough estimate in my head if I need to keep an eye on it.” – Jim Murray, 2003 Dodge diesel, 2013 Lance 855

“I always hand-calculate miles per gallon.  I divide the miles traveled by the gallons of fuel consumed.” – Bert Berry, 2008 Ford F250 diesel, 2008 Sunlite 850SE

“This truck and camper combination are new to us as of May 2011.  We purchased the combo with 49,000 miles on it, it now has 90,000 miles.  I have always hand-calculated the gas mileage using an application on my smartphone called Fuel Log.  Since 2011, our average with the 41,000 miles is 10.26 mpg.  The fuel milage meter in the dash is usually off with a higher reading.  By the way, I tried the Fuelly online application that you guys use and I got the same reading.” – Gerard Pascazio, 2008 Ford F350 diesel, 2010 Eagle Cap 1160

“I have hand-calculated fuel mileage from the first day I bought the truck in November of 2007.  Every fill-up I record the odometer reading, distance traveled since last fueling, number of gallons pumped, and then divide distance by the gallons filled to get mpg average.  It has always been less than what the dashboard indicates.” – Richard Balling, 2008 Ford F250 diesel, 2007 Bigfoot 25C94

“On a trip from upstate New York to Charleston, South Carolina, totaling almost 2,000 miles, the truck managed an average of 11.25 mpg, based on actual miles and fuel purchases.  I couldn’t say how that compares to the computer, as I never bothered to check.  That’s a bit better than the 8 to 10 mpg it manages in local use without the camper.” – Alan Hubbard, 2004 Silverado 2500HD gas, 2000 Starcraft Roadstar pop-up

“I have always done the calculations by hand.  I just fill the tank, record the odometer reading, and use most of the tank.  Upon refilling the tank, I note the mileage and the gallons it took to refill it.  Subtract the two mileage numbers and divide the gallons purchased into the number of miles driven.

The only way you could be off is if your odometer isn’t accurate.  This could be caused from running tires that aren’t the size recommended on the door plate, or an inaccurate speedometer/odometer.  I like to check the mileage tests often seen on the interstates, or at least see if the highway signs showing miles to a particular city are accurate.

My rig gets 15 to 17 mpg unloaded and 11 to 13 mpg with the camper on.  It’s the old school IDI (indirect ignition) 7.3.  It’s a slug on the grades but a real solid power plant!” – Dave Reynolds, 1992 Ford F350 diesel, 2001 Lance 1030

“I have used several different trucks with the on board fuel computer and I have never found them to be accurate.  I always calculate mine by hand using pen and paper.  I am getting around 11 miles to a gallon now and that’s with a truck with 209,000 miles on it.  I don’t know how this compares as I don’t pay attention to the computer fuel mileage.  If you are looking for accuracy, I would also check the odometer and speedometer to see how accurate they are.  Most cars, even new ones, are up to six percent off.” – Ron Tennyson, 2004 Chevy 2500 HD diesel, 2014 Arctic Fox 865

“Funny thing you ask.  You see, the Chevy and GMC trucks are notorious for having bad gas sensors.  So, I know I can get about 350 miles to the tank.  I set my trip odometer to zero and fill the tank every time.  When I fill up I divide gallons into the miles thus giving me miles to the gallon.  The head winds on the Great Salt Flat, not so good.  Tail wind south bound on the 99 out of Sacramento, California, great!  It’s on the list to fix the sensor.” – Thomure, 2000 GMC Sierra 2500 gas, 1994 Lance Squire 8000

“I use the dashboard fuel data.  With the camper we usually average 14.5 MPG.  Hope it’s not 10 or 11% lower!” – Dennis Nord, 2005 Silverado 2500 diesel, 2004 Northern Lite

“Over the summer we took a trip from California through Arizona, New Mexico, Texas and then on to Chicago.  I spot checked the actual mileage against what the dashboard gauge said.  I found that the actual mileage was anywhere from one to three miles less than what was indicated on the gauge.  I attributed the range to the type of road conditions (flat versus hills) we were driving in.  The bottom line is the gauge is just a general indicator of what your mileage actually is.” – Henry Yoneyama, 2006 Ford F350 diesel

“Since I was 16, I always use a calculator to figure my gas mileage.  The auto makers over the years have had some device that that tries to measure mpg.  None of them are accurate.  My Dodge has a “lie-o-meter”, and it says I average 21.3 mpg.  Fat chance.  Using a calculator, I average 17 mpg.  I was very surprised that you didn’t hand calculate as I read your article.  I will say, your “lie-o-meter”, is a lot more closer to reality than my 2006.  Love your magazine.  One day when I can afford it, I hope to have a camper.” – Richard Ciuffetelli, 2006 Dodge 2500 diesel, not yet

“Currently I hand-calculate with pen and paper the mileage because my truck does not have a dashboard calculator.  I range from 16 plus mpg with the camper alone to 10 to 11 plus mpg with the camper and 22 foot boat in tow.

If I had an on-board calculator, I would use it as the sole means of calculating the mileage.  I’m not overly concerned about the mileage calculations one way or the other.  For planning purposes, I use 10 mpg for calculating the number of gallons and cost, based on an estimated average per gallon cost.” – Dave Riddle, 1997 Dodge 2500 diesel, 2006 Host Tahoe

“I use the dashboard, which is about 9 mpg towing a 44′ fifth wheel that’s about 18,000 pounds.” – Robert Mayton, 2014 Ford F-450 diesel, 5th wheel, no truck camper yet

“We use the Road Trip HD App for all our truck costs.  We track fuel and maintenance.  We affectionately call our dash display the “Lie-O-Meter”.  It has enough trouble with the outside temperature.  We would never trust it for mpg of miles to empty. Even with the 4″ lift and 19.5 tires we average 11.5 mpg with the camper loaded.” – Philip McEachen, 2000 Ford F-350 diesel, 1998 Bigfoot 10.4

“I have done both and Ford is so close I stopped hand-calculating the mpg.  Both my Fords were .1 or .2 off.  Your fuel mileage is all dependent on whether the wind is against you or at your back.  Lance came out with their front nose piece and stream-lined the front.  I went from 10.4 mpg with an 1181 to 13.3 mpg with an 1172.  We weigh out 14,700 pounds and travel at 68 to 70 mph.” – Neil Steirer, 2008 Ford F350, 2015 Lance 1172

“I have had the truck since 2003 and use pen and paper.  I do a lot of dispersed camping in north central Pennsylvania driving on hills and state forest dirt roads.  I get 11 to 14 mpg.  The readout has always been between two and four mpg better than actual, and sometimes as much as six mpg.” – Terry Mechler, 2001 Dodge 2500 diesel, 1989 Sunline 11’6”

“I get between 11 and 12 mpg, and that is figured by hand and very close to the dash board. 12.2 mpg was the average on a flat land trip to the Iowa rally.  I go down the road at 12,700 pounds wet.  Mountain driving and wind seems to have biggest effect on mileage.  The dash figure is best when left to calculate over the entire trip.” – Mike Pascucci, 2011 Chevy 3500 diesel, 2012 Adventurer 86FB

“For every vehicle I own (currently four) I keep a log book.  Everything is logged, from changing the oil or even a windshield wiper, with date and mileage.  Every time the vehicle is fueled, that is logged with time, date, mileage, location, brand of fuel, gallons, price per gallon, and cost of the fill-up.  Every vehicle also has a calculator with the log book.

While I might calculate mileage for any single fill-up, I derive what I consider that vehicle’s mileage by calculating number of gallons used over about 5,000 miles.  The Dodge Cummins dually gets a hand-calculated average of 16 mpg while hauling the camper.  I find that surprising, as that was my average mileage on my previous Dodge Cummins, which was a 2500 model, when the truck was not hauling anything.  The dually gets 18 to 19 mpg running empty.

The only thing I can attribute the better mileage of the dually to is that it is a six-speed manual versus the automatic of the 2500.  In both trucks, however, the overhead display read one to two gallons higher mileage that what I hand calculated.” – Oleh Melnyk, 2004 Dodge Ram 3500 diesel, 1996 Bigfoot 2500 9.5

“When we installed the Transfer Flow 60 gallon tank, our truck’s computer no longer knew how much fuel we carried.  Transfer Flow contacted Ford to see if there was a way to reset the truck’s computer, but there wasn’t.  So we now get a warning that we have only fifty miles of fuel left when in fact we are good for several hundred miles.

We note mileage, the amount of fuel added each time we fill up, and keep track of mpg data in a spreadsheet with a graph to show trends.  Over the 50,000 miles with the camper at about 70% highway and 30% off road travel, our overall average is 9.45 mpg.” – George Dunstan, 2010 Ford F450 diesel, 2009 Lance 1055

“We hand-calculate our fuel usage every fill-up.  We use pen and paper and calculations in our head.  Our truck’s dash is usually fairly accurate, but it is interesting to note that we can get dramatically different fuel economy using different brands of diesel.  We usually average 18 miles to the US gallon fully loaded and often towing the boat.” – Tricia Mason, 2009 Ford F350 diesel, 2008 Montana Ponderosa 9.5

“We keep a log of each trip which includes our fuel.  My dash data is usually within .5 of our actual mileage, which we do with a calculator or with pen and paper.” – J. Kevin McCarron, 2013 Ford F350 diesel, 2013 Northern Lite 10-2 CDSE

“My 350 with a diesel gets 11.8 to 12 mpg loaded and 18 mpg empty.  I have an Excel spreadsheet that I enter location, miles, gallons, and total cost.  The spreadsheet then computes tank mileage, accumulated mileage, and accumulated cost per mile.  The truck does not have a mileage computer on board, but my car does.  The car computer is pretty close if you let it accumulate data over time, but if you reset it frequently it varies a lot.

As for your low economy numbers, try several tanks of premium fuel.  The low octane numbers in regular fuel will force the computer to de-tune the engine.  Also, the performance of ethanol supplemented fuels will generally cause a drop in fuel economy of 10 to 20 percent.” – George Hughes, 1999 Ford F350, 2004 Arctic Fox 942

“My truck calculator matches very close to my hand calculator mileage, but my speedometer reads about two miles per hour low.  The odometer appears to be accurate when compared to a GPS.  Have you checked the accuracy of your odometer?

I try to check it over at least a 100 mile stretch.  Our average on a trip around Lake Superior this fall was 12.5 mpg and the truck had only 750 miles on it when we left.  So we hope it will loosen up a bit yet.  I’m always looking forward to your next issue.” – Dave Miller, 2015 Ford F350 diesel, 2003 Bigfoot 10.6E

“I’m old school and have always calculated my fuel mileage by hand. My old truck does not have the dashboard mpg feature.  I wouldn’t believe it anyway!   My mileage averages about 13 mpg with the camper on.  Thank you both for all the work you do.  I enjoy the magazine!” – Scott Barker, 1999 Dodge 3500 diesel, 2015 Lance 1050S

“Excellent question.  We are actually considering a new or newer truck and maybe a a newer full four season camper.  So we’ll be keenly interested in reading the results of the survey.

As you can probably guess by the age of our truck, it doesn’t have a built in mileage calculator.

I do it the old fashioned way.  I keep a paper log book and write down the information with every fill up.  I also keep all the receipts.  That way I also know when and where we were and can determine how different elevations effect our mileage. Downhill to level driving along the coast is best.  The best we can seem to get with our 454 gasser is 10.2 mpg.  Most of the time we were around 7.5 to 8 mpg.

I was a bit disappointed in your results, but not surprised.  I had a Jeep Grand Cherokee with a HEMI.” – Dave Pracht, 1994 GMC Sierra K3500 gas, 1987 Lance LC900

“We use a gas book to track the date, price, total cost, gallons, and current mileage.  To get the most accurate numbers, we fill up every time.  This data is then entered into an Excel spreadsheet that I set up.  Because we also use the truck at home without the camper, I make notations in the book and the Excel file for all the trips we take.

It also includes if we took a trailer and, if so, which one.  I also note if we took the bike carrier and, if so, was it on the front or the rear.  I write the destination(s) and how many people were with us.  I track everything from trip totals, annual totals, and lifetime totals.  It’s very interesting to see our cost per mile go up or down as conditions change.  The numbers I get do seem to be close enough for me to trust the on-board computer.

Depending on the terrain of our trip, and the package we are driving, we get from 7 mpg to 10 mpg.  The scariest number of all is the lifetime cost of the fuel over the last nine years.  But we wouldn’t trade it, considering all the wonderful adventures we’ve had.” – Bruce Scott, 2006 Ford F350 gas, 2005 Northern Lite 10-2000CD

“My old beast doesn’t have a computer or even a trip odometer.  The old girl gets 10 mpg city or highway, with the air conditioning on or off, towing or empty.  I’m sure I won’t be the only one to remind you that even one tire size above stock throws the speedometer and odometer off by as much as 10% which reflects in lower mpg readings, computer or not.” – Gary Usher, 1978 Ford F250 gas, 1983 Coachmen

“The displayed mpg value on the dash doesn’t match with my pen and paper calculations.  But there is a coefficient value that I can change via the dash display that brings the displayed mpg value in-line with my calculated values.” – Daryl Hawkins, 2015 Mitsubishi Fuso FG, Converted Morgan Cargo Body

“With my first five tanks I did both and confirmed that the on board computer was right on.  It’s also dead on when it tells me how many gallons I’ve burned when I drive into a fuel station.  That helps me compute how much cash I need to pre-pay to fill it up, which saves about $.10 per gallon.” – Jim Cornwell, 2011 Chevy 3500HD diesel, 2012 Lance 1191

“If we are talking to other people, we tell them our fuel mileage from the dashboard fuel mileage gauge.  For our own purposes, we calculate it using an HP-12C calculator, but only to three decimal places.

The truck’s fuel gauge varies with the kind of trip (short or long), ambient air temperature, atmospheric pressure, humidity, brand of fuel, speed the truck is driven, the driver (Audrey gets better mileage than Jon), and wind speed and direction.

We then input all this information into a least-squares regression analysis model.  To date, the HP-12C and a little Kentucky Windage always produce the best results.” – Jon and Audrey Hunstock, 2008 Ford F250 diesel, 2014 Northstar 8.5 Arrow U

“Since I bought my truck and camper ten years ago, I have kept a running tally of the mileage.  I have a sheet of paper on my center console and record manually the date, mileage, gallons, price and the calculated miles per gallon.  I just simply subtract the odometer miles from the previous fill-up and divide by the number of gallons at the pump.

Typically, the dashboard is always lower than my calculated value.  It varies from being almost dead-on correct to as much as ten percent off.  Typically it is about four to five percent off.  My mileage with the camper on a flat highway running about 65 mph is about 11.5 mpg.” – Larry Routt, 2005 Ford F-350 diesel, 2004 Lance 820

“I hand-calculate, with usually the calculator on my phone.  I do log all miles driven and then divide miles by gallons.  Since I have a tuner on the truck, the miles per gallon isn’t correct at all on the truck display.  It seems to be reading double what the actual mileage is.  I know that the truck display is cumulative also.  So it is an average on good mileage and bad mileage.  This display can be reset though, and this can give you a much more accurate reading on any specific trip, and load.

The best mileage of my truck unloaded was 16.1 mpg.  With the camper, the best milage was 11.5 mpg.  With the camper pulling a car trailer with a Pinzgauer, it was 9.5 mpg.  I have all the power I need though with 7.3 Power Stroke.

Gordon, I assume the Dodge mileage readout can be reset and may give you a more accurate result.  The manufacturer’s mileage prediction is always deceiving because the way they drove the vehicle in lieu of the way we drive our vehicles.  Good Luck.” – Gary Bell, 1999 Ford F350 diesel, 2000 Lance 1130

“I use what the truck tells me as I just use it as a close tracking tool.  I never have checked out the real mileage, but now I am wondering how close the Ram is.” – Marc Swanson, 2014 Ram 1500 gas, 2011 Northstar Igloo

“I trust my fuel mileage indicator in my Dodge.  Most of the time when I fill up, the readout shows destination to empty of about 430 miles.  Depending on how much foam goes into the tank and how quick it dissipates, usually determines the DTE to empty readout.  Sometimes it shows 390, a few times it was at 510 (probably on a day when I filled the tank very slowly trying to avoid foam build-up).

In terms of fuel mileage with the camper on, driving around town in stop and go traffic, the readout shows 12.2 to 12.4 mpg.  On a straight highway stretch with the cruise control set at 62 mph I have readouts of 13.3 to 13.5 mpg.  With a good tailwind I have been as high as 14.6 mpg.  But with strong headwinds, I’m running 11.3 to 11.7 mpg.  With this question I think I will do the hand-calculated method for the next two fill-ups.” – Roger Odahl, 2008 Dodge 3500 diesel, 2004 Eagle Cap 950

“I hand calculate to two places.  The over head computer is worthless.  This is my second Dodge.” – Paul Yoh, 2006 Ram 3500 diesel, 1994 Lance Squire 8000

“Actually, I do it in my head then compare it to the dash readout.  It’s right around 10 mpg on average.  Since we live in the White Mountains of New Hampshire, it depends on terrain.” – John and Cathy Strasser, 2012 Chevy 2500HD, 2012 Lance 855S

“I hand-calculate.  My truck does not have dash calculation.  I fill up and use three-quarters of the tank, and then fill up again.  I take the miles driven and divide by gallons used.  I average 15.2 mpg with the camper, and 19 mpg without camper.” – Sam Tardo, 2002 Ford F250 diesel, 1997 Shadow Cruiser

“We do both.  The dashboard read outs are good for general relative data, as in, “will I be saving anything by driving 5 mph slower that I was a few miles back, or I wonder if this new headwind is affecting my mileage?”.  Those situations aren’t trying to tell me what the truck is accurately achieving other than a comparison against different operating conditions.  The hand-calculated, paper, pen, calculator, is good for absolute figures over the long term.” – Jeff Johnston, 2004 Nissan Frontier, Four Wheel Camper (planned)

“My on-board electronic calculator quit years ago.  While it did work, it was always off.  That is why I never had it fixed.  Hand-calculating is the only accurate method.

Fuel gauges are a rough estimate also.  My belly or my butt usually tells me it is time to fill up.  I currently avg 12 mpg.  My best was 15 mpg with an Oklahoma tail wind.  My poorest was 9 mpg with an Oklahoma head wind.  I keep my speed 65 or less.  My engine does its best work below 2100 rpm.  I also pull an aluminum motorcycle trailer with one or two bikes on board.” – Larry Kelly, 1999 Ford F-350 diesel, 2015 Palamino Backpack Edition 8801

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