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Calculated MPG

marpel
Explorer
Explorer
Have read a number of posts, in different site forums, describing posters hand calculating their mileage.

Some post that they record details at every gas-up and have kept meticulous records since they purchased their trailer/fifth wheel (for years), to show the exact MPG.

I suppose I can understand doing so for a short time after acquiring a particular truck/trailer combo, to then know that combo's MPG, in various conditions.

But, what is the purpose of going beyond that nice to know? And, has doing so caused anyone to change their driving habits or impacted a decision to choose a particular route to their destination?

Just curious.

Marv
49 REPLIES 49

valhalla360
Nomad
Nomad
MarkTwain wrote:
Old Mark Twain proverb "If you have to worry about MPG or have to ask the price of fuel, you probably should give up RVing" :):):)


Follow the nickles & dimes and the dollars tend to follow.

If you do 3-4 local trips per year, it doesn't prove much. If you are doing 10-20k miles per year, upping the MPG by 1-2 is a few bucks in your pocket. That's very doable by driving more efficiently.

As others have said, it can be an early warning sign. A few years back we returned from overseas after the winter and the first drive into town, she was only getting 10mpg (not towing). Nothing felt odd but stopped and checked. One of the rear wheels was hot. Swung by the repair shop we use and they found the brakes were dragging.
Tammy & Mike
Ford F250 V10
2021 Gray Wolf
Gemini Catamaran 34'
Full Time spliting time between boat and RV

ajriding
Explorer
Explorer
You do know that if you know your mpg then you can calculate the cost of a long trip and plan your budget. If you do not know if RV gets 20 or 3 or 12 then you just hope you are rich enough to not care if gas cost $1,000 or $500 or $2,500...
Is it cheaper to get a hotel and eat out for a trip or take the RV? the MPG people know...

Also, a sudden change in mpg might indicate issues that you can correct early or that will help the mechanic diagnose after a break-down.

I think these types of reasons are why people care, but does not mean that others should care about their mileage.

PA12DRVR
Explorer
Explorer
I tend not to worry too much about the price of gas or MPG. If I get too wigged out about it, I go for a flight in the ol-PA-12. 8-9 gallons per hour, circa 9 - 10.5 mpg, circa $6/gallon of 100LL Avgas in Los Anchorage, more like $7.50 or $8/gallon in the boonies. $60 - $70 per hour fuel cost makes the 15-16 mpg I get in the F250 look pretty good.
CRL
My RV is a 1946 PA-12
Back in the GWN

BackOfThePack
Explorer
Explorer
The other data useful is in recording engine hours as Average MPH is a better clue to vehicle use over strictly MPG. One divides odometer miles by engine run time to see what the days trip took as against clock time. (Zero idle time assumed).

Time spent at steady-state is lower than one expects. So, Average Speed and what you think of as Travel Speed start to diverge strongly when running too fast for conditions (lane-changing, use of throttle to do more than steady-state; ANY use of brakes save exiting road).

This is really about Quality versus Quantity. Going faster doesnโ€™t mean one gets there faster (average speed may barely budge), but that the wear & tear penalties on vehicles and operator canโ€™t be justified.

In the end the thing to have is GPM (Gallons Per Mile). When that varies 10% low (one has earlier found correct travel speed), then itโ€™s an early indicator of mechanical issues to investigate.

As to the dash digital MPG read-out โ€” as I know the variance with mine versus actual โ€” re-set gives me a picture of changed winds. Run a touch faster or slower to maintain the standard GPM.

Other feedback devices (Engine Load Percent; or Manifold Pressure + EGT; or Vacuum + GPH) are helpful.

MPG records โ€” alone โ€” arenโ€™t as useful without Average Speed + GPM.

A familiar route 323-mile day is right at 54-MPH Average and overall .066/GPM.YMMV

.
2004 555 CTD QC LB NV-5600
1990 35โ€™ Silver Streak

deltabravo
Nomad
Nomad
gbopp wrote:
If you keep track of your MPG and you notice it decreasing, you know there is a potential problem before it becomes a problem


The above is why I have done it.

There was one vehicle I had where if I saw the MPG go down, it was time to do some sort of maintenance on it... it was so long ago, I don't even recall which vehicle it was or what the maintenance was.

It became habit, so I just keep doing it.
2009 Silverado 3500HD Dually, D/A, CCLB 4x4 (bought new 8/30/09)
2018 Arctic Fox 992 with an Onan 2500i "quiet" model generator

way2roll
Nomad III
Nomad III
ppine wrote:
A few mods made it possible. AFE air intake, 4 inch exhaust and an SCE tuner.
Not snake oil. Simple improvements and careful driving.
Measured by filling up the tank, driving 400 miles and filling up the tank again to do the calculations.


So $1,000 in performance upgrades. You didn't mention that.
2023 FR Sunseeker 2400B MBS

Grit_dog
Nomad III
Nomad III
And ppine returns!
2016 Ram 2500, MotorOps.ca EFIlive tuned, 5โ€ turbo back, 6" lift on 37s
2017 Heartland Torque T29 - Sold.
Couple of Arctic Fox TCs - Sold

way2roll
Nomad III
Nomad III
ppine wrote:
Keeping track of mileage has changed my style of driving. Now I am more of a hyper-miler and slow down ahead of time and don't accelerate that hard. Use cruise control when it is safe. That is how I got to 23.8 mpg in a one ton Ford diesel.


You driving downhill constantly with the wind at your back?
Owning a 2020 one ton Ford diesel with the 10 speed tranny and live near the shore which means it's flat. Do a good bit of highway travel and in a year and a half of ownership I have never seen 23.8.
2023 FR Sunseeker 2400B MBS

JIMNLIN
Explorer
Explorer
A 23.8 mpg from a single tank calculations from a one ton diesel is possible....just short fill the fuel tank at a fuel stop that has a down hill slope in the right direction causing the short fill/other scenarios for fantastic one tank mpg is very possible. Or use the DIC mpg down slope figures on I-70...I-80 east from the highest elevation in NM/CO/WY.
I've gotten some great mpg from Raton NM Pass at 7800' elevation and east on US-64/US-412 down to eastern OK elevation 685' @ 668 miles.
And going up the same way nets 3-4 mpgs less....and of course which way the 38-42 mph winds are blowing.

I prefer a average mpg check over several tanks of fuel such as our 1260 mile one way annual trip to UT and return the same routes. All pencil figures.
"good judgment comes from experience, and a lot of that comes from bad judgment" ............ Will Rogers

'03 2500 QC Dodge/Cummins HO 3.73 6 speed manual Jacobs Westach
'97 Park Avanue 28' 5er 11200 two slides

ppine
Explorer II
Explorer II
A few mods made it possible. AFE air intake, 4 inch exhaust and an SCE tuner.
Not snake oil. Simple improvements and careful driving.
Measured by filling up the tank, driving 400 miles and filling up the tank again to do the calculations.

dedmiston
Moderator
Moderator
ppine wrote:
Keeping track of mileage has changed my style of driving. Now I am more of a hyper-miler and slow down ahead of time and don't accelerate that hard. Use cruise control when it is safe. That is how I got to 23.8 mpg in a one ton Ford diesel.


Sounds legit.

2014 RAM 3500 Diesel 4x4 Dually long bed. B&W RVK3600 hitch โ€ข 2015 Crossroads Elevation Homestead Toy Hauler ("The Taj Mahauler") โ€ข <\br >Toys:

  • 18 Can Am Maverick x3
  • 05 Yamaha WR450
  • 07 Honda CRF250X
  • 05 Honda CRF230
  • 06 Honda CRF230

ppine
Explorer II
Explorer II
Keeping track of mileage has changed my style of driving. Now I am more of a hyper-miler and slow down ahead of time and don't accelerate that hard. Use cruise control when it is safe. That is how I got to 23.8 mpg in a one ton Ford diesel.

dedmiston
Moderator
Moderator
Segal's Law

A man with a watch knows what time it is. A man with two watches is never sure.

2014 RAM 3500 Diesel 4x4 Dually long bed. B&W RVK3600 hitch โ€ข 2015 Crossroads Elevation Homestead Toy Hauler ("The Taj Mahauler") โ€ข <\br >Toys:

  • 18 Can Am Maverick x3
  • 05 Yamaha WR450
  • 07 Honda CRF250X
  • 05 Honda CRF230
  • 06 Honda CRF230

Brooksbc58
Explorer
Explorer
I have 2 speedometers, 2 fuel gauges, and 3 odometers in my truck. I'm never quite sure how far I've driven, or how fast I got there.