ISM 500 vs ISM II 500

[Mike Canter]

A question for some of you experts. In 2004 Cummins designated the motor as the ISM 500 then in 2005 it was designated as the ISM II 500. Does anyone know what was changed in the motor to change the designation?
Thanks

[Steve Ownby]

Morning Mike,

Thanks for your service. The tier designations were related to emissions requirements and they seem to be used on off road equipment only. If there is any difference involved in an engine designated tier II it is probably in the ecm programing. The ISM with cooled egr which was designed to meet the '04 emissions standards was the design used until the '07 standards. The ISM is being replaced by a smaller redesigned ISX. It's too bad because the "M" is a great engine.

Steve O
'03 Monaco Signature w/ ISM

[Mike Canter]

Thanks Steve. The ISM II designation was in athe original literature of a 2005 Navigator. I agree in that the ISM motor was probably the best motor ever put in a motorhome. According to some Cummins mechanics I have talked to it is a 800,000+ mile motor and the ISL was a 475,000+ mile motor. Needless to say even full time driving one should not wear out either if one stays away from that 2006 ISL with the bad rods.

So have you had any problems with your ISM?

[Steve Ownby]

My ISM and drive train has been completely trouble free. In fact the whole chassis has been trouble free (knock wood). I sent an oil sample to Blackstone lab last fall after a 12000 mile trip to Alaska & got a perfect report card. I need to do a transmission fluid change this winter along with the annual items.

Steve O