Excessive diesel fuel consumption 99 eagle

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Craigspeer2001

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Mar 12, 2018
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11
Ok I didn't expect this thing to get like Prius fuel economy but it's only getting 3mpg.  It is a 99 American eagle with 8.3 350hp isc cummings, average speeds is 65mph mostly interstate miles  very little to no steep grades it has 95k miles on engine fresh oil change and all filters are new accept air filter  and I have a new one before next trip too take place. The dash air is broken so no load from that and haven't used gen set yet because it has been cool enough not to need it. I would like too at least know what too look for before I start, is that just the best it's going to do I was hoping for at least 8mpg.  Engine rpm is 1700 at 65. Yes it's new to me I had a gas class a before and it wasn't as nice are as big but it got decent fuel milage for a 25 year old rv and being 35ft it get close too 8mpg.
 
Yes, that is extreme excessive, but having no said that. Pushing 65 on an old rig is bound to drag you down .
My rig is weighs 10k and gets 10mpg.. so... maybe you could squeeze out a gallon or two but not much.
 
You should be closer to 7ish I would think. That air filter could do it if its plugged so see how it does with a new filter. (your rig weighs more than mine but we're both running 350hp - I get 7 pulling a full size pickup)
 
Really confused about weight title says one thing 24,000 chasis tag in coach says gvwr 31000 I was wrong on the 35k. I did get old air filter off today looks horrible hopefully that's it.
 
Craigspeer2001 said:
chasis tag in coach says gvwr 31000
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Interesting. I gross at 33, but scale about 29,500 so close enough for comparison. Hopefully it was that filter. If the filter really looked bad you may want to consider an earlier oil change next time, that was probably pretty dirty oil and you can't get 100% out during a change. I would suggest oil and coolant analysis also after you've put a few thousand miles on the oil (you could do coolant analysis now)
 
Yes my dad is own me about putting additive in coolant know and the filter is really nasty. What really has my concerns is I drive it 550 Mike's home in 200 buks in fuel all flat land from Florida. I drive it last weekend 160 Mile's it drank 150 buks in fuel I was like what happened different really nothing in my mind sticks out I have about 300 miles on oil change previous owner appears to have taken good care of it just lil cosmetic issues so far.
 
Craigspeer2001 said:
Yes my dad is own me about putting additive in coolant
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I would suggest you not just put in additive before you get coolant tested. The test will look for the additive, and tell you if the coolant is good for continued use. You don't want to dump additive into bad coolant. Also the test will tell you if you have other issues.

You may want to consider new coolant so you have a fresh start. Expensive, but with the additive will last you a very long time. If it was mine, unless you had a receipt from the previous owner showing it has fresh coolant, I would pull a sample from the old to see if there are any issues, then I would drain and fill with new.
 
Scott gave good advice there, and it would do you well to heed it. I would recommend taking it to a shop the works on Cummins' and pay the couple/few hundred to check everything. Explain about the recent oil/filter change, and the new air filter. Get them to check fuel pressure(s), and the coolant. Any decent shop will have a standard hit list to follow when giving a diesel a "physical"
 
Just a thought, I had problems with my old 300hp 8.3 cummins and after fixing a list of things it is now much better with more power. The turbocharger waste gate was locked up in the partially open position, exhaust manifold leaks were reducing the flow to the turbo and the exhaust brake was hanging partially closed. After fixing all of that it had so much more boost that it blew off a connector to the air intake precooler. Just thought those would give you some things to check especially since it won't hurt to have a look at those areas also. You also might want to check you precooler for holes and clamps/hoses for tightness or cracks.

Mine had what looked like a squirrels nest in the air filter and the intake hoses to the filter were made from flex hose and restricted flow enough that it would set off the filter indicator. Replaced all the hose from filter to inlet plenum with 6" pvc pipe and enlarged the plenum and opening...getting very close to 10 mph on flat ground w/no wind and staying around 60mph.
 
Yes, 3 mpg is awful. That coach with the ISC should be in the 8 mpg arena, even at 65+ mph (60-62 is much more economical). At a guess, your turbo is not functioning, the exhaust brake is stuck, or the air filter is clogged. Any of those would make the performance poor - lousy acceleration and poor mpg.  It's not unusual for the exhaust brake control arm to get stuck on that vintage - they need regular lubrication and few get it.
 
I also remove/replaced my muffler with a SS straight Thru resonator type and adjusted the fuel return up in pressure and replaced two 90 degree elbows in the exhaust track with 45s..That damn muffler weighed 75 pounds after removal. I also went to Michilin XZA2 rear tires that are slightly over sized 22.5s by about 4%... I now  average 10 mile per gallon.>>>Dan
 
I have a date for March 26 with repair shop they going to check valves and doo a thorough inspection of my rv also checking coolant and fuEl as well.
 
I realize this may be a few week old thread but just saw it and thought I would suggest another item to look at, brakes.  I had a friend that bought a coach that had sat for a while and he also complained about fuel consumption being excessive with the same 8.3 Cummins engine.  Upon my inspection I found the brake S cams were corroded so severely that they were not releasing and the brakes were dragging.  It was all new to him coming from a gas coach but upon my first drive I noticed the boost seemed to be quite high and then found the brake issue.  Tore them apart and cleaned up, replaced S cam bushings and cleaned linkages and it rolled freely again.  Mileage also came right back up to the 7-8 range.

Mike
 
Vavles adjusted one code in transmission relaced air filter and ful filter replaced all air bags and leveling vales 8.3 mpg know
 
Good deal  :))  and thanks for the update - you?re back in the ballpark. Now the question is, what are you going to do with all that extra gas money?  ;) ;D
 
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