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Sunsetranch · 07-05-2022, 05:29 PM

Been looking at a lot of older rigs 2006-2009 seems like many engines have developed issues when emissions standards tightened. Just found a 2007 with the ISX 525 have not found much written about this one unlike many others. Hoping that is good news…looking for some feedback on this engine, good, bad or ugly? Owner says this engine is older as factory often had older ones around in those years.

Smitty77 · 07-05-2022, 07:31 PM

The devil is in the details... If the ISX is EGR only (Usually CM870 build), these engines are not as potentially problematic as the later years ISX's with EGR + DPF (Usually a CM871 build).

A 2007 coach, could have either engine, depending upon how early in the Model Year the coach was produced.

The CM871's ISX's were the ones you could have read about that had the 'Dropped #6' valve. Due to the soot/gook build up in the Exhaust/EGR/DPF plumbing - working it's way down and dripping onto the #6 (And sometimes #5) Valves. A corrosive effect kicks in, and can result in the valve breaking down and taking out the cylinder - and more. Cummin's did come out with a new and improved cylinder head with inconnel alloy's, that handles the soot/gook drip.

Seems like the addition of DPF in the CM871 build, resulted in the block being installed at a slight angle leaning towards the #6, and that is why it is more of a chance of having problems.

Usually the ISX600 and 650 are the ones you read about with the #6 Dropped Valve issue. But some ISX600's and 525's with CM870 builds, have also reportedly had dropped valves too. (And this is from memory, as I believe a Monaco owner posted in this section about an ISX525, which I believe had EGR only, had Dropped it's Valve... BUT FOR SURE DO SOME SEARCHES on that, as I'm going from memory 3-4 years ago. I've never personally met or communicated with an owner of an ISX600 EGR CM870 engine that lost a valve.

And, on the Over The Road Truckers forums, Rawze's is one such site, the ISX did not seem to have as many reports of Valve's Dropping. The thought was because they were putting lots of miles on their engines, vs an RV'er that may due 10-15K in a busy year.

The 'Smog Plumbing' of both the EGR and DPF were basically counter productive... Pumping Engine Exhaust back into an engine, not too swift of an idea. As the EGR's start having problems, the engines run dirtier and dirtier, lower MPG too - thus the counter productive comment.

Me? I made a decision to go with an ISX600 EGR only CM870 build engine, in our current coach. I had planned to go ahead and have Cummins swap out the head's with the new and improved head, at time of purchase. But instead, put about 65% of the cost of doing so, into as good as possible Extended Warranty that covers the full coach, and chassis. My point, is I went into the purchase with open eyes, and feel I've established a reasonable counter measure to the chance of an engine Dropped Valve event - which from my research, was very low on the ISX600 with CM870 build engine.

Opinions will vary

!

Good luck on your hunt,
Smitty

vito.a · 07-05-2022, 09:43 PM

Smitty captured the details well.
We've owned two coaches with the Cummins CM870 ISX 525. A 2007 and a 2004. The engines are almost identical with just EGR (exhaust gas recirculation) emissions. Both engines were great.

Some folks think that the bigger engines will use more fuel but that's just not true. Almost all large diesel coaches get from 6-8mpg and the biggest variable is driver technique.

Monaco did stockpile engines and used a lot of 2006 model engines in 2007 and even 2008 coaches.

I've found the newer gear reduction starter makes starting a breeze.

When you get a coach when one of these large diesel engines the entire drive train is upgraded. It has the Allison MH4000 transmission that is nearly bullet proof.

Wish you all the best!

Sunsetranch · 07-06-2022, 10:30 AM

Since all the ISX are susceptible to the valve drop, is there any way to have engine inspected up front that would determine if engine is showing signs?

vito.a · 07-06-2022, 01:11 PM

Quote:

Originally Posted by Sunsetranch

Since all the ISX are susceptible to the valve drop, is there any way to have engine inspected up front that would determine if engine is showing signs?

The short answer is no. The #6 exhaust valve is the primary culprit. Some folks have unsuccessfully tried to get a camera in there. If you are going to disassemble the engine to inspect it you might as well update the parts.

Your choices:
1. Preemptively replace the cylinder head with the new part number that has upgraded valves and seats. If the engine is the CM871 650hp version, it will also need new piston scrapers.
2. Purchase an extended warranty that covers engine repairs.
3. If the engine is the CM870 (especially the 525hp) version chances are very slim it will have an issue so you just take it as is.
4. You can find a private shop that does heavy diesel work and remove the cylinder head and just replace the exhaust valves with a higher quality (keeping the original head).
5. Address the EGR system which causes the problems.

Hope this helps!

Sunsetranch · 07-06-2022, 03:17 PM

Its the ISX 525 waiting on engine number from seller...
Thanks

Sunsetranch · 07-06-2022, 09:25 PM

Got engine serial number to check with Cummins but from picture, also it reads ISX 525 and then " MC/05" does that mean anything?

pbensen · 07-28-2022, 01:29 PM

Quote:

Originally Posted by vito.a

The short answer is no. The #6 exhaust valve is the primary culprit. Some folks have unsuccessfully tried to get a camera in there. If you are going to disassemble the engine to inspect it you might as well update the parts.

Your choices:
1. Preemptively replace the cylinder head with the new part number that has upgraded valves and seats. If the engine is the CM871 650hp version, it will also need new piston scrapers.
2. Purchase an extended warranty that covers engine repairs.
3. If the engine is the CM870 (especially the 525hp) version chances are very slim it will have an issue so you just take it as is.
4. You can find a private shop that does heavy diesel work and remove the cylinder head and just replace the exhaust valves with a higher quality (keeping the original head).
5. Address the EGR system which causes the problems.

Hope this helps!

Vito, this is well written with one exception. It's the intake valve the that breaks not the exhaust valve. I'm sure it was just a typo>