RRUGG wrote: I compared the overhead with hand calculating over two tanks of gas. Both represented about 300 miles of driving. All highway driving was 55-60 mph. Both tanks included about 25 miles of non-highway driving, mostly cities & small towns. The first hand calc was only 1/10 of a mpg lower than the overhead. The second hand calc was 1.9 mpg lower than the overhead. Curious that there would be so much variation. Ample reason to do the hand calc and ignore the overhead.
No, ample reason to ignore the calc (which is very inaccurate except when averaged over MANY. MANY fillups). There is just no way to fill your tank EXACTLY to the same level every time. It can be off by a gallon or more depending on the nozzle.
The overhead computer use the same sensor that measures the fuel to your fuel injectors and this is VERY accurate (or you engine would run like krap).
BTW, the thermometer on your overhead display uses the same sensor that the engine computer uses to determine ambient temperature.
All the sensors in an engine have to be very accurate (when functioning properly). It is easier for the manufacturer to hook these existing sensors to a display than to have a second set of inaccurate ones just for the display (just to make the "Chinese junk conspiracy theorists" happy).
Paul (Mouse)
2007 Flagstaff Shamrock 17 Hybrid (heavily modified for boondocking and winter camping).
2007 Dodge Dakota Quad Cab 4x4, 4.7L HO, factory tow, 3.92 gears.
Equil-i-zer Hitch, Prodigy.
Yamaha EF2400 Generator (quiet, cause I care!)
MIne is usually up to .5mpg optimistic compared to the calculator. I use it mainly as a reminder to keep my foot out of the loud peddle and to coast as much as reasonably possible. I compare the OH to the calculator every once in a while. Once it was even .1mpg less than calculated.
'05 2500HD Dodge 5.7L Hemi 5spd auto/3.73 SLT. 96k miles
ex '95 Cummins,'98 12v Cummins,'01.5 Cummins,'03 Cummins
'07 KZ Jag 28JFSS.
I love accuracy myself that's why I set my watch with my atomic setting clock. Resets itself by radio every night. But, I can't much change the truck only my driving habits to improve or ruin my mpg. I check my computer reading and compare it to hand calculations if it is close that is all I need to know. I know how to drive get the best mpg. I still love to look at it though!
Let's all just get a life!
I hand calculate always. My three GM's with the DIC it is always off, as I have always except one fill have put 1 to 2.5 US gallons or 6 to 12 more litres, than the DIC said that I have used.
The DIC fuel economy was recorded or computed if you will on the lesser or programmed amount.
The DIC always (Except once this must have been the angle thing or air lock or shady gas pump) it reports better mileage than I really get towing or not. Maybe the diesel DIC are better.
2005 2500 Avalanche
2004 30' Terry Quantum 290FLS
Equal-i-zer,Prodigy
Calgary Alberta
Bumpyroad wrote: I assume you mean that the fillups in between don't have to be completely topped off, etc.
bumpy
Yes. Glad you know what I meant.
...and not using the initial fillup - thats cheating! Shame on you.
I posted my average from our Florida trip 2 weeks ago. It was 11.48 over 1801 miles. The only 'real' way to know would be to drain the tank and actually measure what was used. I think we all accept 'topping off' as accurate as we can get without draining the tank. The more miles and gallons, the greater the accuracy will be.
Bruce & Carolyn Wittmeier
Viet Nam Vet 1968-69
2001 Ford F250 4X4 OffRoad, Auto ESOF, KingCab, ShortBed, Airlift Airbags, DiPricol gauges, SCT-Tuner from DP-Tuners (40/80/120HP), Bilsteins, Reese Slider, Jordan, 2001 30RKFS SunnyBrook w/personal touches.
I used to be fascinated by the gauge on my dad's old Caddy. when coasting it would go up to the 80s IIRC, when mashing it, down to the single digits.
and that initial fillup was to get a starting point, zeroing out the mileage.
bumpy
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