Community Forums

gimlimike · 08-05-2017, 05:49 AM

As a newbie can someone give me some broad brushstroke differences between the two, thanks. We are shopping now and that info would be great to have

Cruzer · 08-05-2017, 08:33 AM

The Cummins ISM is (was, actually) a 10.8 liter engine, typically produced in the 500 HP version for motorhomes with 1,550 lb-ft of torque. The ISL is an 8.9 liter engine, produced with horsepower ranging between 350 and 450 HP, with a ton of 400 HP versions being made. The ISL has 1,.200 lb-ft of torque, although the latest years now have 1,250.

Both are good engines. The ISL is very popular and about as bulletproof as it gets. The ISM was discontinued when the EPA 2007 emissions came in and replaced by the ISX12 engine. Obviously, the extra torque and power was welcomed, especially on the heavier 45' coaches.

The only downside I've heard of on the ISM is that they use a dry PTO shaft. This shaft drives the air compressor and isn't lubricated by the engine oil, like the other engines are. That's because it's not at the front of the engine in the timing cover where it gets splash lubrication from the engine oil. Instead it's a rear takeoff back by the bell housing so it has sealed (aka - dry) bearings. That's fine until they fail after a number of years and miles. When that happens it's a real bear (labor intensive) to get to them to replace the PTO shaft. Not so bad on a line truck but extremely difficult on a motorhome due to the bedroom floor. The newer ISX12 didn't have that problem.

tom chelbana · 08-05-2017, 08:45 AM

We have a 04 Essex with a 500 ISM with a EGR valve which was installed on ISM'S starting in 2002. Great motor but did have EGR valve problems in the early years. First problem with check engine light and low boost came in year 3. Cummins replaced valve under warranty and then around year 5 same issue again and we replaced valve and paid 1500$ since out of warranty. This was a revised/upgraded valve and have no problems since. First valve had 30K miles and second valve 60K miles and now have 137K miles. When Cummins went to the ISM from the M series engine they changed the fuel system and other up grades. I think first ISM came out in 2000 and in 2002 switched to ISM-2 with EGR. Better to get ISM without EGR but will be older coach. Glad we have ISM engine and has worked well for us for the 137K miles. Did replace turbo myself at 125K miles. All ISM EGR motors come with a variable turbo which does give quick boost.

spuds · 08-05-2017, 08:15 PM

Quote:

Originally Posted by Cruzer

The only downside I've heard of on the ISM is that they use a dry PTO shaft. This shaft drives the air compressor and isn't lubricated by the engine oil, like the other engines are. That's because it's not at the front of the engine in the timing cover where it gets splash lubrication from the engine oil. Instead it's a rear takeoff back by the bell housing so it has sealed (aka - dry) bearings. That's fine until they fail after a number of years and miles. When that happens it's a real bear (labor intensive) to get to them to replace the PTO shaft. Not so bad on a line truck but extremely difficult on a motorhome due to the bedroom floor. The newer ISX12 didn't have that problem.

The pre-DEF version of the ISX (2007-2010) has the dry PTO problem. A well-documented issue for Country Coach (they made a wet kit available). A stealth issue on any Foretravel that has that engine (through the 2012 IH45) and a number of folks have had it fail - it takes out the cooling fans and Foretravel won't offer any assistance for this known problem.

I haven't heard of a dry PTO with the ISM (and no one on the Foretravel forum has mentioned it or we'd know). We had an ISM in our 2003 Foretravel with no issues.

Michelle