450 ISM Fuel Mileage in a 45' Tag Axle

[Scottybdivin]

I know, another fuel mileage topic. Getting close to pulling the trigger on a 07 MADP with 450 ISM. My current rig, F350 and 18K 5th wheel, has averaged 8.4 mpg over 15K loaded miles. i track it relentlessly as well as the empty stats (13.4). I am planning to tow a F150 CC 4x4 behind the MH and drive 60-65.

[palehorse89]

here is another thread going on http://www.irv2.com/forums/f278/corn...on-228634.html about mileage........

[Scottybdivin]

Yeah, I saw that one and the 2 dozen others before it. LOL. I was just hoping for something more specific to the 450 ISM.

[Gordon Dewald]

I moved from a 450 with 18,000 trailer to a 450 ISL. I pull a 13000 stacker. Mileage for the two is about the same loaded.

Like travelling in the MH way more than the truck and 5er. Jury is out when we get where we are going.

[Scottybdivin]

Originally Posted by Gordon Dewald

I moved from a 450 with 18,000 trailer to a 450 ISL. I pull a 13000 stacker. Mileage for the two is about the same loaded.

Like travelling in the MH way more than the truck and 5er. Jury is out when we get where we are going.

That's the kind of information I was looking for. Thanks. Can you quantify it?

[tom chelbana]

We have an 04 Essex with 500 ISM with tow 49K and getting on average 7 MPG. You can go to Cummins have 450 ISM upgraded to 500 and when at Spartan an owner said he increased his mileage .5. We travel around 62 to 65 MPH which is 1450RPM.

[joelyn5]

Have an 11 Essex. Coach weighs 44,300 with all our stuff. Towing a 5,000 lb GMC Acadia. At 60-65 I've averaged 6.6 MPG going from Virginia to Michigan to Dakotas then south to Arizona and CA.

[Scottybdivin]

Originally Posted by tom chelbana

We have an 04 Essex with 500 ISM with tow 49K and getting on average 7 MPG. You can go to Cummins have 450 ISM upgraded to 500 and when at Spartan an owner said he increased his mileage .5. We travel around 62 to 65 MPH which is 1450RPM.

That would be acceptable. I wonder if the return (7%, 50 HP, 100 FP) is worth the investment?

Have an 11 Essex. Coach weighs 44,300 with all our stuff. Towing a 5,000 lb GMC Acadia. At 60-65 I've averaged 6.6 MPG going from Virginia to Michigan to Dakotas then south to Arizona and CA.

I wasn't sure when they stopped making the ISM or M11. I have a good friend that works for Cummins in R&D. His job is to abuse them and try to break them on the bench. The cut them up and send them to the scrap metal bin. He thinks the ISM may be the best engine they ever made.

[Steve Ownby]

Originally Posted by tom chelbana

We have an 04 Essex with 500 ISM with tow 49K and getting on average 7 MPG. You can go to Cummins have 450 ISM upgraded to 500 and when at Spartan an owner said he increased his mileage .5. We travel around 62 to 65 MPH which is 1450RPM.

My results with an ISM 500 built in late '02 is very similar to Tom's. My life time mpg is 7.8 and I suspect the difference is largely that my engine doesn't have an EGR valve. These engines are superb in motorhome service. Cummins field engineers and techs love them because they are relatively trouble free and easy to work on. The EGR was a source of problems early on but by '07 that problem should have been solved.


Steve Ownby
Full time since '07

[Gordon Dewald]

Originally Posted by Scottybdivin

That's the kind of information I was looking for. Thanks. Can you quantify it?

Truck (6.0 L 325 hp 29,000lb) and trailer with 50,000 miles makes about 8.5. Mh (ISL 450 48,000lb)with 6,000 miles is making 8.3. I expect the MH will get slightly better with a few more miles. I drive the MH a bit faster (60 - 62) than the truck (55- 60).

[Scottybdivin]

Originally Posted by Gordon Dewald

Truck (6.0 L 325 hp 29,000lb) and trailer with 50,000 miles makes about 8.5. Mh (ISL 450 48,000lb)with 6,000 miles is making 8.3. I expect the MH will get slightly better with a few more miles. I drive the MH a bit faster (60 - 62) than the truck (55- 60).

If I get north of 8 mpg pulling a F150 with a golf cart riding piggyback, I would be stoked. Thanks for the information.

[Ronrad]

I have a 4521 07 mountainaire and get 7 mpg pulling a full size 2014 Chevrolet Silverado high country. Flat or mountains make no difference.


Sent from my iPad using iRV2 - RV Forum

[Gordon Dewald]

Originally Posted by Scottybdivin

If I get north of 8 mpg pulling a F150 with a golf cart riding piggyback, I would be stoked. Thanks for the information.

IMO it has a LOT to do with the size of the shoe on the foot controlling the unit. I drive with slippers.

[RV Norm]

The difference between my F350 with 15k lb trailer and the ISM 500 with a 49k lb RV and 10k lb is nill. Probably around 7-8 mpg either way.