throgmartin Posted June 12, 2020 Share Posted June 12, 2020 I recently read where a coach owners ISX 650 blew up. It was once again a dropped valve. I passed the story on to my son who is a certified Cummins tech asking what the issue is with these ISX engines. To help some of you I thought I would pass this on to you here. He taught me years ago to keep my RPM's at around 2000 whenever climbing grades. Now I see why. This is what he said: " The ISXs had a lot of problems and they went on for years. This particular failure is a combination of weak valves combined with pushing too much HP/torque for an RV application. I know they came out with a new design for valves, heads and I’m pretty sure they have a newer “carbon scraper” / APR - Anti Polish Rings to help keep the liners in tact. They also revised the calibration to derate, I believe down to 600HP - it’s not a 650HP engine. One problem is the torque demand. A lot of RVers are all about fuel economy and try to keep those Allisons in as high a gear as possible up grades. The torque curve peaks at around 1500 and many will try to keep the RPMs as low as possible, but you are placing the most stress on the internals at that RPM. Grabbing a lower gear and doing 1700-1800RPM is much more desirable. It’s the same reason you get more momentum in a lower gear, your temps are lower at higher RPMs, etc. For whatever reason, some people either don’t connect the dots or ignore it because they think lower RPMs are better for the engine / fuel economy. The ISX at those numbers are prone to snapping valves under stress. Happened to truckers too that ran ‘em hard under low RPMs in high gears up grades and such. " 1 2 Link to comment Share on other sites More sharing options...
John Haggard Posted June 12, 2020 Share Posted June 12, 2020 Learning to manual shift. Solves lots of problems Link to comment Share on other sites More sharing options...
throgmartin Posted June 12, 2020 Author Share Posted June 12, 2020 Yes John it does. My son and an old trucker taught me years ago how to climb a grade. Preparation is the key. At the bottom of a grade and just before heading up I start downshifting. They told me to downshift and get the RPM's around 2,000 and keep downshifting to keep it there. Not only does this reduce stress on the engine but also keeps the temp's down. 1 Link to comment Share on other sites More sharing options...
miniedmo Posted June 12, 2020 Share Posted June 12, 2020 Thanks Throgmartin, I am just learning to drive in the mountains around my neck of the woods and this is really good information. 1 Link to comment Share on other sites More sharing options...
DavidL Posted June 29, 2020 Share Posted June 29, 2020 From my readings on irv2 forum, the ISX issues may be temp or acid related and not necessarily to weak valve springs. And it could be a couple of the many thousands of ISX owners that have had an exceptional problem ($30K repairs) that gets the attention of others that "blows the issue out of proportion". None of the occurrences have had definitive root cause identified. So I would call it a forum click bait topic only at this point. Link to comment Share on other sites More sharing options...
Ivylog Posted July 8, 2020 Share Posted July 8, 2020 I learned of the ISX #6 intake valve issue a couple months after buying a 08 Navigator with a 06 ISX 525 engine 2 years ago. A higher % of MHs are having this problem than trucks and the higher HP (600-650) are dropping the valve more often. They are not snapping the valve off, the perimeter of the valve breaks off usually getting the piston and the turbo. I know of two 525 HP, 06 or older, that have dropped #6. Hopefully the better valves and seats will stop the acid created by the EGR gasses from weakening the intake valves...$20K if you do it preimptpley and $30+K after it breaks. the EGR 1 Link to comment Share on other sites More sharing options...
Ivan K Posted July 9, 2020 Share Posted July 9, 2020 (edited) Just curious, what do you mean by "the perimeter of the valve" ? Is it the sealing portion of the valve. Wonder why/if anyone has not come up with a EGR delete kit for it, dirty but cheaper fix as on the smaller truck engines... Edited July 9, 2020 by Ivan K Link to comment Share on other sites More sharing options...
Ivylog Posted July 9, 2020 Share Posted July 9, 2020 (edited) Yes, the pictures of the broken #6 valves has chunks of the outside perimeter ( sealing surface) missing. I’ve been told a 1.25” metal freeze plug fits nicely into the EGR tube where it bolts to the engine intake tube. Edited July 9, 2020 by Ivylog 1 Link to comment Share on other sites More sharing options...
Ivan K Posted July 9, 2020 Share Posted July 9, 2020 There you go, sounds a little too simplistic and I know it is past the grey zone so I leave it at that. Thanks for the reply. Just my curiosity... 1 Link to comment Share on other sites More sharing options...
Kent Madison Posted December 31, 2023 Share Posted December 31, 2023 I picked up a used 09 Navigator with the ISX 650 and 80,000 miles about 3 months ago. On the way south for the winter I dropped the number 6 valve and totally destroyed the engine. It has been at Cummin's in Las Vegas for the last month and a half getting a completely new engine at the tune of over $70,000. So much for a good deal on the home. We believe that this home set in Florida through a few bad storms and had not been ran for several years. Cummin's said that the entire engine has rust throughout it and was not rebuild-able. When it is all said and done we will be about at the retail price on NADA only do to the fact that we where well below to start with. But we will have a new engine with a complete warranty. The take home message is a motor home with a diesel pusher engine and lots of mileage on it just might be a better deal in the long run as these big engines like to be run and run a lot. 2024 will be a year of travel for sure. 3 Link to comment Share on other sites More sharing options...
dl_racing427 Posted January 2 Share Posted January 2 On 7/8/2020 at 8:10 PM, Ivan K said: Just curious, what do you mean by "the perimeter of the valve" ? Is it the sealing portion of the valve. Wonder why/if anyone has not come up with a EGR delete kit for it, dirty but cheaper fix as on the smaller truck engines... I'm sure they have, but the EPA has been cracking down hard on smog defeats, and the fines are getting astronomical. 😱 Link to comment Share on other sites More sharing options...
Ivylog Posted January 2 Share Posted January 2 Perimeter/ circumference of the valve breaks off. I’ve read that a $3 metal freezer plug will block the EGR where its tube bolts to the intake tube. Link to comment Share on other sites More sharing options...
Recommended Posts
Create an account or sign in to comment
You need to be a member in order to leave a comment
Create an account
Sign up for a new account in our community. It's easy!
Register a new accountSign in
Already have an account? Sign in here.
Sign In Now