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Old 02-10-2017, 12:27 PM   #1
Join Date: Nov 2016
Posts: 21
6MPG's :(

I took my skoolie out for its maiden voyage yesterday. Nothing crazy, 40 miles out of town and back. I had no mechanical issues and learned a lot about the direction I want to go with the rest of my build. I also learned how lousy my MPG's were . My bus has the 6.9 idi and the at545 both are in great condition. Tranny shifts with no hesitation and the 6.9 (180k) runs great does not smoke thanks to a recent tune up.
I was expecting low MPGs (im getting 6...) but im having a hard time wrapping my head around putting any more money into a vehicle that will cost me approx. $50 to go 120 miles.
I have not messed with the injection pump or anything related to timing. Its a short bus and weighs 12k empty the rear end I believe is a 5.37? or something like that?
Any ideas? Turbo? Re-gear? is something else wrong that im missing? does anyone have a similar experience with the same motor and trans set up?
Thanks for any help. I would like to fix the issue if there is one rather than buy an entire new bus.
87mackd is offline   Reply With Quote
Old 02-10-2017, 08:25 PM   #2
Join Date: Jan 2017
Posts: 12
Well, I had a 6.9 in a f250 4x4 and when new it struggled to get 14 mpg highway. I know the turbo conversions did a bit better (Banks, etc) but nothing like a 5.9 cummins that did 22 in my 1989 Dodge with camper. Can you put taller tires on it? My 6.9 had 4.11 and I changed to 36" tires, it helped a lot.
Bus ted1 is offline   Reply With Quote
Old 02-11-2017, 12:49 AM   #3
Bus Crazy
Join Date: Jul 2011
Location: Winlcok, WA
Posts: 2,195
I suppose my first question is how you arrived at your 6 MPG while only going 40 miles. The amount of fuel you can squeeze into a tank or where the pump will shut off each time is not a fixed amount. I have seen some tanks that would take an additional 10 gallons after the pump shut off and the same tank another time not wanting to take even one more gallon.

My next question is how did you arrive at the 40 mile figure. If you were relying on the bus odometer I would first double check it against mile posts or GPS to determine how much more or less than a mile it is clicking off each mile. The Feds allow 10% either way so you could have gone 1.1 miles for every mile or 0.9 miles. For that matter, if it has different diameter tires than what it had when it left the factory the odometer could be even farther off.

A lot of factors could be causing lower fuel mileage:
  • Tires not inflated enough
  • Front end not aligned properly
  • Brakes adjusted improperly and dragging
  • Exhaust system with blockage/muffler with baffles broken
  • Air filter restricted
  • Air intake restricted
While 6 MPG may sound pretty bad to you, we had buses with big gas engines that routinely got less than 2 MPG.

I think most people with buses the size of yours with engines like yours get 7-9 MPG. I doubt you will ever see 10 MPG.

Good luck and happy trails!
cowlitzcoach is offline   Reply With Quote
Old 02-11-2017, 08:33 AM   #4
Join Date: Nov 2016
Posts: 21

Cowlitz: I filled the tank before I left and filled it upon my return. I calculated the distance to my destination and doubled it for the return. Upon my return (to the same gas station I filled at) I filled the tank to find out how many gallons I had used, then factored it in to the total distance traveled... it actually came out to 6.2 ha! I know there are some factors that might give or take 1mpg, I just couldn't believe it was that low! Its a 20gal tank so assuming that at 6mpgs I have 120 miles per tank . Which on a 80 mile (round trip) is within my range for my calculation.
The only thing I did not check that you mentioned is the tire inflation. other than that the motor got a complete tune up, I suppose the exhaust system could be an issue, Its 2 into 1 right now, ive been thinking of making it a 2 pipe straight back no muffler, its a 4 in exaust tho so I don't think theres a point in going any bigger. Maybe that will help?
Been considering turbo as well, but kits are 2k plus.. I paid 1500 for the entire bus.
I guess I could just learn to live with it, but it doesn't sit right with me that it would cost me $250 to travel 600 miles, that's a plane ticket.

Bus-ted: I think for any real change id have to either change the gears or tires, I am new to bus type tires so im not sure what is available, however I know they are 11-22.5, im not sure I can go any taller
The way I see it is gears are going to be the only thing that make a difference, but im concerned if I make the gears to high ill have a problem with hills. That 6.9 is gutless as it is.

Im just not sure which direction to go, do I turbo it? Do I change the gears/tires? Do I try and open my exhaust up or mess with my injection pump? Oh it also wont do over 60mph.. that's fun.

Either way thanks for your input!
87mackd is offline   Reply With Quote

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