As my sig states, I have a 94 5.9 cummins. The truck now has 166,000 miles on it, and I have had it since the end of February. I love it, and am still learning about the truck.
I have two questions, one related to temperature, and the second related to the automatic.
1) I have noticed, after paying more attention to it, that the temp guage fluctuates between 155 and 190 degrees. The needle will slowly rise to 190, then go back down to 150-155, and then slowly rise back. Doesn't seem to be related to pulling a grade. The antifreeze level is where it should be. Should I assume that I need to replace the thermostat, or is this typical of the Cummins?
2) Tempermentally, the auto sometimes does not want to stay in O/D or converter lockup. If I shut the truck off and start it back up, it will behave itself for a while. The transmission was rebuilt about a year and a half ago, and does great. I am thinking it is an issue with the PCM- anybody concure with that, or have another idea?
Thank you in advance...

 

I can't answer the 2nd question but I can answer the first. It is normal. What you are seeing is the thermostat opening and closing. The location of the temp sensor is in a place that it will see the difference between when there is cool coolant coming from the radiator and when it hot because it is just recirculating in the engine. No need to be concerned at all.

 

Thanks for the quick reply, and good news. As for the second question, I will eventually be replacing the PCM, because the truck has a shudder at certain speeds, and there is a service bulletin about it, with an upgrade PCM called for. I am just wondering if the replacement PCM will remedy the hunting.

 

Your PCM is likely fine, problem is the TPS
read this http://dodgeram.org/tech/transmissio...TPS_adjust.htm

If you need a new TPS they are about $150 from Napa.