ChrisJohnson

Back before all the mods in my sig, and the truck was mostly stock, the best mileage I ever had was 21.5 mpg. This is actual mileage, not the overhead, filled up to the edge of the filler neck, using actual miles traveled, and actual number of gallons to top the tank back off to the edge of the filler neck. I used to have to make the same trip back and forth from Corpus Christi TX, to New Orleans LA many times in my former job. It was always about 570-580 miles to the motel I used to stay at, then just a couple of miles more in the city the next day to take care of my business, then top it off and head for home. The time I had the best mileage was when I made a very concentrated effort to follow all posted speed limits on the trip, using the cruise control as much as I could, and not stopping at all (teeth were really floating by the time I got to N.O.!). Top speed was no more than 70 mph. The normal way I would usually make the trip, was to set the cruise control when I was at 2000 rpm's which would usually put me at 71-71.5 mph. And then make stops along the trip as needed. That would net me anywhere from 19-20 mpg, depending on traffic conditions. The overhead would always read 4-6 mpg higher. There have been other times going to different destinations where I would go over 600 miles, and still not set off the low fuel light. But I would try to not do that to often. Since I put on all the mods you see in my sig a couple of years ago, and haven't had to travel for work anymore, I have no idea what I get for mileage anymore. In fact, I don't think I want to know, it would probably depress me to much!

Rednax

I agree about percentage and should have stated it that way (my number was from highway miles alone). I tend to change the overhead several times over the course of a tank, so have not checked it the past 10k or so. Will do.

But, as the only number worth worrying about is the overall fuel burn -- the total over all miles; the average -- the real use of the overhead, for me, is to spot check roads/loads and prevailing winds; their effect on the trucks present fuel burn.

Changes from tank-to-tank mean little except as a way of spotting problems (declines of 10% or better) when no other changes have occurred (use, territory, etc).

I like your speculations, above, and will recall them. CUMMINS says something similar about the road monitor on their big motors not being dead reliable until 140k miles. Converging curves of true use and calculated use.

Diverging curves would be pretty funny if we could make a case for it (and the Ferd guys don't find out).
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