This week-end, I replaced a few parts in my cooling system. One of them was the thermostat. Thinking along the lines of your regular car owner (not used to working on diesels yet), I went to NAPA for the part. However, after reading the workshop manual, I noted that there should be three jiggle pins in the thermostat, and the NAPA part just had the one. Deciding to play cautious, I returned the $7.99 part and went to the dealer. He didn't have one, but quoted me a price of $35 for the part. I nearly died. I recently found a Cummins service center near me, so I went there. Found out a few things I thought might be interesting.
1. Cummins said that in the first Gen series engine, there were three different thermostats that could have been fitted. I had to read him the engine number before he could tell me which one was mine. Did anyone know that?
2. After reading the manual again, I realized that the thermostat seems to work backwards to the way a normal gas engine thermostat works. By that, I mean that when the thermostat opens, it sends water back through a by-pass to the water pump inlet, by-passing the radiator. If the thermostat fails in the open position, which I think all gas engine thermostats do, the engine will overheat. Does the Cummins thermostat fail closed? I've never heard of this before, but that would mean it could be dangerous to put a gas engine thermostat in a Cummins.
3. The Cummins price for the same thermostat was $40. By this time I was over the sticker shock, but I guess if the part really is special the price may be justified. But, are all Cummins parts this expensive?

John