Truck Repair: Engine wont shut down, newmar motorhome, ambient air temperature

Question
I have a 2003 Newmar motorhome with a Cat 3126 engine, Freightliner raised rail chassis, Allison 6 speed transmission and when it is hot outside, the engine will not shut down when I turn off the ignition. Once I waited 1 1/2 hours and then it shut down.

I had a Freightliner mechanic out to see it and he suggested that it was a particular relay that was intermittently failing. I have replaced all of the relays that have anything to do with the ignition system and I still have the same problem.

I noticed that the box under the front hood where the relays are gets very hot. I open it up because I have to pull a relay to get it to shut down. When this happens the engine is at low operating temperature but the ambient air temperature is in the 90s or higher. I am currently in Mexico near the Guatemala border and headed to Panama and expect it to get hotter as I go. The next time it won't shut down I am going to put an ice bag on the relays and see if they shut down.

Any ideas?

Kathe Kirkbride


Answer
interesting. cat is all electronic so i am sure its not caused by the engine electronics.i suspect that your coach manufacturer has hung so many devices on that system that it is near capacity, and getting hot causing it to hang up. i take it removing this relay shuts down instantly. my only advice is to remove this relay, seperate the wires to it, and remount a heavier relay as a far from the others as possible. you may also have a problem in the ground of that and other relays, such that power is reversing and powering it from the ground resistance of all those others. so lets ground the panel with a heavy wire right to the chassis.