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Old 02-10-2017, 12:27 PM   #1
Mini-Skoolie
 
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.

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Old 02-10-2017, 08:25 PM   #2
Mini-Skoolie
 
Join Date: Jan 2017
Posts: 20
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.
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Old 02-11-2017, 12:49 AM   #3
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Location: Winlcok, WA
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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!
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Old 02-11-2017, 08:33 AM   #4
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Join Date: Nov 2016
Posts: 21
indecision

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!
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Old 05-08-2024, 06:50 PM   #5
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Join Date: Sep 2017
Location: Swansboro,NC
Posts: 3,007
Year: 86
Coachwork: Thomas
Chassis: Ford B700
Engine: 8.2
Rated Cap: 60 bodies
i know? i know?
could not get my thread starter to work for whatever reason and decided to grab this old thread because the last post was from macked and i want to here yalls opinion on a mack power train i have a chance to get.
i have a chance to get the entire mack tractor with the t675 engine 235/237 hp with a 5 speed manual tranny. entire truck for a parts swap and a real good price and i have recently worked with the man over the last few months at work and trust what he says mostly.
sight unseeen i want to go look at it.
any thoughts or opinions on the engine and tranny?
my searching has said that this engine pairs well with the 5 speed.
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Old 05-08-2024, 07:01 PM   #6
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Location: Swansboro,NC
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Year: 86
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Chassis: Ford B700
Engine: 8.2
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also meant semi tractor and it runs. needs tires but already needed that for my big bus but upgraded rims and and the entire truck for parts to swap over.
just gotta make room in the driveway but can park it right next to the big bus and have full driveway access for a forklift after mommas little bus is out of the way and my 77 truck goes to the back yard. aint ready for it project wise but a few projects can be rescheduled.
not my wifes bus though.
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Old 05-09-2024, 08:39 AM   #7
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Join Date: Nov 2014
Location: NM USA KD6WJG
Posts: 1,342
Year: 1991
Coachwork: Bluebird
Chassis: All American RE 40 FEET
Engine: Cummins 8.3
I'v driven them in the past. They had a very wide power band and good fuel economy. They also had some kind of engine brake too. One of them had a air assisted clutch to help the girls drive them.
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Old 05-09-2024, 07:33 PM   #8
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Join Date: Sep 2017
Location: Swansboro,NC
Posts: 3,007
Year: 86
Coachwork: Thomas
Chassis: Ford B700
Engine: 8.2
Rated Cap: 60 bodies
its more HP than what i have.
is the engine and the 5 speed worth the swap from 8.2 and the 545 i think it is what will work for me but want to have opinions.
man says sinchro. tranny 5 speed dont know rear gear and used to use it for a low boy trailer. didnt ask what he hauled but in a farming community..
i have the 8.2 4 stroke at 175 hp on my big bus with the 545 and a 6.5 rear end 49 mph with a stick on the gas pedal nfor cruise.
dont kinow rear gears on this truck but motor and tranny i think should be an upgrades and a road tractor the rear end upgrade should be a no brainer even if a tag axle.
now i am at which project first and how to make room in the driveway for a road tractor while i finish my wifes little bus?
is the engine and tranny worth the effort to put in a school bus?
mechanic wise i am golden just asking if the powertrain is worth it for a skoolie the only 49mph by design as ordered from the county.
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Old 05-09-2024, 08:18 PM   #9
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Join Date: Nov 2014
Location: NM USA KD6WJG
Posts: 1,342
Year: 1991
Coachwork: Bluebird
Chassis: All American RE 40 FEET
Engine: Cummins 8.3
What is your parking brake set-up now? Is it a brake on the back of the Allison?
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Old 05-10-2024, 01:52 PM   #10
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Join Date: Sep 2017
Location: Swansboro,NC
Posts: 3,007
Year: 86
Coachwork: Thomas
Chassis: Ford B700
Engine: 8.2
Rated Cap: 60 bodies
air brakes.
i didnt think about what kind of brakes the mack truck has i just assumed air brakes
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Old 05-10-2024, 02:10 PM   #11
Bus Geek
 
Join Date: May 2014
Location: West Ohio
Posts: 3,775
Year: 1984
Coachwork: Bluebird
Chassis: International 1753
Engine: 6.9 International
Rated Cap: 65
I say go for it. I'd love to see the swap! That mack will be a lot longer then your 8.2. Plan on setting it back into the bus and building a dog house around it. The endt engine had a few decade run and was pretty popular, so I don't think you'll have issues with it. I've long wanted to do a semi engine/trans/axle swap in mine. Sounds like your donor is cheap enough, what are you waiting for?
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Old 05-10-2024, 02:14 PM   #12
Bus Crazy
 
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Join Date: Nov 2014
Location: NM USA KD6WJG
Posts: 1,342
Year: 1991
Coachwork: Bluebird
Chassis: All American RE 40 FEET
Engine: Cummins 8.3
I'm with Booyah on this one. It would be easy to swap to a OD road ranger too.
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