The biggest issue with MPG calculation is many people use "first click" when the pump shuts off as believing the tank is full! With diesel this is simply not the case.

Diesel foams a lot and will vary a lot depending on temperature, flow rate, blend and filler location. It was maddening to fill my Breakaway when I first got it, it would shut off after 20-30 gallons. Then for the next 20-30 minutes had to nurse it along until I had liquid sitting stable in the neck, another 10 to 15 gallons could be added.

After changing the filler location on the tank from the back, half way up to the front top of the tank, I now go all the way to 45 gallons but still have to slowly fill the remaining 5 gallons +/- to get liquid stable in the neck.

fuel filler change

Having the coach level is another consideration for accurate MPG calculations. Slower speed (around 55 MPH) helps, pulling a toad or trailer can help but generally at higher speeds because of drafting, but at slower speed will have a negative effect. Hilly country and towing will really kill MPG.

With my Breakaway, I have averaged 10.1 MPG over 220K miles of driving. Going anywhere East I go up mountains, some to 7000', and as I have repeatedly said I drive fast >65 MPH <75 MPH.

5.9L Cummins 230 HP, 6 speed Allison, 4.0:1 diff

Very true Ed. Gas stations are rarely level, so it is difficult to get an accurate consistent number. My mileage with the 3208TA generally runs between 8-9 range. I’m running 65 mph at 2000 rpm. This is with a GPS speedometer.
Randy

quote:

Originally posted by Randy76:
My mileage with the 3208TA generally runs between 8-9 range. I’m running 65 mph at 2000 rpm. Randy

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What transmission is in your Barth Randy? I am at about 52 miles per hour when running 2000 Revolutions per minute on the Caterpillar. I have never seen 9 miles to the gallon in my Barth. My Barth shifts in to 4 gear at 52 miles per hour. The fuel mileage log I have dating back from 1995 shows between 6 and 8 miles per gallon.

Kevin, mine is the Allison MT 647 4 speed. Probably like yours. Where the difference may be is the differential ratios. I’ve tried to find the ratio numbers on mine, but in all the information I have, have not been able to do so. I think my maximum 3-4 shift speed is around 58 mph. Low to mid 8’s is my typical mpg. Remember your coach is 4 ft longer/heavier than mine.
Randy

Randy, where are you located in Nor/cal? I am near San Jose

Hi Ed. I live about 120 North and East from you in Calaveras county near the town of Angels Camp. It would be fun catching up with you sometime.
Randy