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

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, 03:41 PM   #2
Bus Crazy
Join Date: May 2014
Location: West Ohio
Posts: 1,498
Year: 1984
Coachwork: Bluebird
Chassis: International 1753
Engine: 6.9 International
Rated Cap: 65
Most get around 10-12 in a full sized bus with that engine and trans. Yours should be close to that if not more. I'd say you have something wrong but where to start is anyone's guess.
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Old 02-11-2017, 08:37 AM   #3
Join Date: Nov 2016
Posts: 21
Right and that is why I feel like something is up. I'm just putting this out there hoping that someone has a similar setup and can tell me if what they are getting is similar. something has to give. I was expecting low mpg's but not that low.
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Old 02-11-2017, 10:57 AM   #4
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Location: Moab, UT
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Year: 3/94
Coachwork: International
Chassis: In Flux
Engine: DT 466 , MT 643
Rated Cap: 84
My buddy Bart has a full size flat nose with that set up and does get 10+ MPG , somethings up for sure ?
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Old 02-11-2017, 01:02 PM   #5
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Location: Calgary, Alberta
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Year: 2001
Coachwork: Thomas
Engine: Cummins ISC 260HP/660Torque/MD3060 6spd
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My 38 foot flat nose with cummins 5.9 ISB and Allison 3000 gave me 6.5 mpg for a 2000 mile drive. I'm not sure what could me my problem.

I'd test yours again and for a longer distance. It could be something as simple as the tank wasn't completely full.

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Old 02-11-2017, 01:59 PM   #6
Join Date: Apr 2013
Location: Near Sacramento, CA
Posts: 39
Year: 1991
Coachwork: Blue Bird
Chassis: International
Engine: DT466 w/MT643
Rated Cap: 71
40' dog nose : dt466 and mt643 with 6:14 rear end. The last couple trips, both 1200+ miles. High desert Grand Canyon, 4 corner, Oregon coast type of driving. We got 7.9 mpg on both. We're governed at 2500rpm's which is 62mph on flat ground and 64.9mph downhill.

For what it's worth, we have an Mercedes '85 300D Turbo Diesel that seemed like a totally different car after a diesel purge. The stuff is actually call Liqui Molly diesel purge. Pretty amazing what's stuck inside something that has so many constantly moving parts.
Heath, Laura and The Kids

Opportunity is missed by most people because it is dressed in overalls and looks like work. - Thomas Edison
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Old 02-11-2017, 02:22 PM   #7
Join Date: Nov 2016
Posts: 21

One thing I haven't really got into, mainly because i didn't think it would have that great of an effect is tire pressure. Does anyone have 11-22.5's? What psi do you run in your tires?
A fuel treatment wouldn't hurt. But I have replaced all 3 fuel filters, cleaned all the injectors and replaced all the return fuel lines.
What about the injector pump? The motor runs great no smoke, like i said, but maybe its something subtle?
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Old 02-11-2017, 02:29 PM   #8
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Join Date: Apr 2013
Location: Colorado
Posts: 1,602
Year: 1993
Coachwork: bluebird
Engine: 5.9 Cummins, Allison AT1545
Rated Cap: 2
i think i do good at about 8mpg, i've had better and worse, but overall, it isn't very good. cummins 5.9 with at545, 4.7 rear @67 mph

11.22.5's running 100-110 psi

i stopped tracking mileage because it was never good news
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Old 02-11-2017, 03:04 PM   #9
Join Date: Nov 2016
Posts: 21
Haha turf, im just about there with not tracking mileage. I love the bus too much to get rid of it. Im looking into getting the IP rebuilt. Ive been doing some research and it turns out 180k on the original IP means it should be rebuilt (100k ago). Even though it runs great with no mechanical problems, it just isn't running efficiently enough it seems. There is a company on ebay that is doing it for 250 or so, just for anyone who is interested.

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Old 02-11-2017, 05:17 PM   #10
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Posts: 1,204
Year: 1999
Coachwork: Bluebird
Chassis: 3800 International
Engine: T444E
Rated Cap: 72
our full size runs about 9-11 mpg, that's running a full tank of fuel, hwy driving around 96kms an hour, seems to be the sweet spot, on a short run I get way less, I also have a scan gauge , real handy. don't get to down about your mpg, wait till you get out on trip, make sure you fill your tank up the same way, with mine it clicks off when full, but then I can squeeze in another 40-50 liters in, I use a flash light and look inside the tank and so I know where the fuel level is , and make sure its the same most of the time. Also if you are heavy of the throttle say good by to your fuel, take your time in joy the ride,
my bus build viewtopic.php?f=9&t=5931
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Old 02-11-2017, 07:28 PM   #11
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Join Date: May 2016
Location: Richmond Virginia
Posts: 932
Year: 1984
Engine: 366 Big block Chevy! :) w/ Stick shift
The bad news is 60mph top speed.... until a sudden stop is needed

On motorcycles we have a saying "It's not how fast it can go, but how fast it can stop."

60mph leaves some good room for error.
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