Abysmal mileage

[Ivylog]

04 Dynasty 400 ISL with side radiator...88K miles, 45,000 lbs, 65-67 mph, 7 mpg. Something is not right unless you are running 75+ mph.

[znt1186]

We have an '05 Mandalay 40e with the 400 ISL. Haven't had it very long, but get about 8 mpg so far. You might also check to see if your fan controller is operating correctly. If it does not work properly, then the fan will run on high constantly. That happened on our previous coach and dropped the mpg down almost 2mpg. Also agree to check all filters and turbo. Even at 75 mph, you should get better fuel mileage.

[Pdvitalis]

Oakcreekeric said, "If you haven't "serviced" your RV since owning it.. a good start would be to take it to a Cummins dealership and have them perform a complete maintenance - baseline it if you will.. then you can see if there are improvements and the technician will have all the basics out of the way and then can concentrate on narrowing down where your problem could be."


Thanks for your kind response. My MH was serviced at I-State Truck Center just before I bought it. They go over everything pretty thoroughly and charge $1100. I had the same service done this spring. I told them about the poor mileage and asked them to check the settings. The mechanic reset the information center that was reporting the mileage, now that doesn't work right. It doesn't report bad mileage anymore either . Unfortunately, the mileage by calculation is just as bad. I think I'll take it to a Cummins center as you suggested and let them take a crack at it.

[Pdvitalis]

Originally Posted by Ivylog

04 Dynasty 400 ISL with side radiator...88K miles, 45,000 lbs, 65-67 mph, 7 mpg. Something is not right unless you are running 75+ mph.

I do have a heavy foot and drive 5 to 10 over the speed limit but it always gets 4.5 no matter what the conditions, long trips, short trips, stop and go or highway.

[Pdvitalis]

Originally Posted by ScoobyDoo

I have found many times the first place to look for bad mileage is between the drivers ears. If you have a big horse that can keep up with traffic, and flog it to prove it you got to feed it.
But your injectors could be leaking.

I usually flog it but I have taken a variety of trips and have intentionally taken it easy for a tank. It doesn't impact the mileage at all; it's stuck at 4.5.

[TonyMac]

Dragging a brake?

[MO Fred]

Originally Posted by funjnt

Yes that does seem low. Our older coach gets anywhere from 7.5-9 mpg. Right now the silverleaf is sitting on 8.5. I wouldn't know where to start but maybe have it scanned by cummins? Does the ecm state any problems? Tire inflation? Lots of variables but yes that seems low.

Same here, 8.5 MPG for us. Wonder if OP is burning too rich and experiencing a lot of black smoke.

[A Traveler]

Something else to consider, and it’s something I have firsthand experience with.

Check the electronic fan control. If the controller has failed, it’s “fail safe” mode is to run the hydraulically powered radiator fan at max speed all the time. Running that big fan at 100% speed 100% of the time will keep your engine nice and cool, but it will cost you 1 mpg.

Guess how I know that... [emoji6]

[jimmy braden]

what is the boost level at 60/1500 rpm in 6th with no toad on level road? IT should be close to 5 psi, 7 at most. If you cant pull 40K lbs with an ISL425 on less than 6psi its not making the power it should. Start with all filters. Then come back. And do a distance traveled divided by fuel fill volume calc just to make sure.

My ISC gets 9.3 to 9.7 at 60 with notoad - 30K lbs and 6psi on level ground.

[AE Wanderer]

I have a 2008 American Eagle 42F, with a 425HP ISL engine. Coach weighs 39,000 pounds. It gets 5.7mpg.

[Dav L]

2002 43' 500hp ism = 7.5mpg driving the speed limit on most highways.
something is wrong if you are below 7mpg.
First: Exactly how are you calculating mileage?

It's not dragging brakes...they would have smoked a long time ago.

[Quincy]

Originally Posted by Mr.Mark

Quincy, the original poster has an '08 coach that has a DPF (diesel particulate filter), so he will not have black smoke at all as that is what the DPF is for. It will capture all the particulate then it will burn it off during a regen cycle.

To the OP, our previous coach was a '08 Dynasty that had the 425 ISL Cummins. We weighed in at 40,039 lbs. and got over 7.0-7.5 mpg on a regular basis. We put almost 70,000 miles on that coach over a 7.5 yr. period and no trouble with the DPF.

Our coach would regen about every 8,000-10,000 miles.

You should have the coach checked out to make everything is OK as the mileage is low.

Good luck and safe travels,
Mark

Thank you for the info Mr. Mark. That means it will be harder to tell if the motor is running too fat or not. JMHO I think that 4.5mpg is not a result of poor driving habits or under inflated tires. I don't see those things dropping the mpg that much.

It will be interesting to find out what the end result of it all is.

[Quincy]

Originally Posted by Pdvitalis

Oakcreekeric said, "If you haven't "serviced" your RV since owning it.. a good start would be to take it to a Cummins dealership and have them perform a complete maintenance - baseline it if you will.. then you can see if there are improvements and the technician will have all the basics out of the way and then can concentrate on narrowing down where your problem could be."


Thanks for your kind response. My MH was serviced at I-State Truck Center just before I bought it. They go over everything pretty thoroughly and charge $1100. I had the same service done this spring. I told them about the poor mileage and asked them to check the settings. The mechanic reset the information center that was reporting the mileage, now that doesn't work right. It doesn't report bad mileage anymore either . Unfortunately, the mileage by calculation is just as bad. I think I'll take it to a Cummins center as you suggested and let them take a crack at it.

I am sorry to say this but I think they owe you 1100 bucks. I still think it may not be going into "closed loop" mode.

[twinboat]

Getting A diesel to just run rich is a challenge.

Sure a few injectors or a badly clogged air filter will contribute to a rich condition, along with a rough running engine, but since diesels don't have throttles and are open to all the air they can pump in, the only thing that controls engine RPM is fuel.

Inject more fuel and the engine goes faster. That's the basics of them.

In a good running diesel, only lugging it will cause black smoke, and since electronic fuel control, that's even been eliminated. They are programmed to not over fuel.

The OP should have a shop connect it up to a computer and get a performance readout. Then go from there.