500 ISM and Allsion 4000, Onan 12500 QD

[moxy1962]

Had a few coaches with ISC 8.3 and ISL Cummins 8.9 with Allsion 3000's and 7500 Onan QD's had great luck so far, looking at a Signature with ISM 500 and Allison 4000, 120000 miles on coach, what am I in for and are there any known problems with either I should be aware off. I typically ensure trannys have life long filters and transynd, always run Rotella T6 oil 15\w\40 in motors and genny,  Not sure of Onan 12500 hours yet, any issues with these that anyones aware off?  

 

Thanks

 

Moxy

[vito.a]

The Cummins ISM 500 and Allison 4000 are rock solid.  Some of the 2003 and newer ISM engines had an occasional EGR cooler failure.  

You may want to reconsider using Rotella T6.  These engine require 10 gallons (not quarts) of oil and run great on Rotella T3.  In fact, Cummins recommends conventional oil.  

How many hours on the generator?  The early Onan 12.5 generators have an Isuzu 3 cylinder engine that is also rock solid.  When they reach 2000 hours most will recommend a belt change and the belt is buried in there.  

The rest of the coach will keep you very busy repairing and updating systems but these are great coaches.  

Best of luck!

[moxy1962]

3 minutes ago, vito.a said:

The Cummins ISM 500 and Allison 4000 are rock solid.  Some of the 2003 and newer ISM engines had an occasional EGR cooler failure.  

You may want to reconsider using Rotella T6.  These engine require 10 gallons (not quarts) of oil and run great on Rotella T3.  In fact, Cummins recommends conventional oil.  

How many hours on the generator?  The early Onan 12.5 generators have an Isuzu 3 cylinder engine that is also rock solid.  When they reach 2000 hours most will recommend a belt change and the belt is buried in there.  

The rest of the coach will keep you very busy repairing and updating systems but these are great coaches.  

Best of luck!

thanks, plenty of experience with older dynastys,, labour of love

[Ivan K]

I have one with the same powertrain.  No issues with it at close to 200k, just maintenance. Generator, 12.5kw Isuzu, at almost 4k hours, beside scheduled maintenance had to replace fuel pump and then recently the stator due to plugged cooling duct. Just humming along. House issues are just as with any other. Love our Sig.

[Ivylog]

I would rate a ISM second to only a DD60. The ISL is a good medium size MH engine…possible exception are those built in 06 wit the wrist pin problems. Last would be the 650 ISX, next to last the 600 ISX, and next to next last the 525 ISX.