Engine/Transmission (1994 - 1998) Rollercoaster temps....OVER

[fortunate1]

My truck has ALWAYS had the fluctuating engine temp needle: builds up to around 180 - 185 and then drops down to ~150 - 160. Repeat the process over & over. It's been discussed on here, and some different thermostats have been recommended to "cure" this. Sometimes the new thermostat works, sometimes not. So I have never really worried about it.



So... in preparing for a weeklong trip to FL, I sprayed degreaser all over the a/c, intercooler, and radiator. Then hosed it all off to clean them. I had done the cleaning mainly to help the a/c keep up with the FL heat. What I found out was that the engine temp stayed put (once warmed up) with the needle just to the left of the 1 in "190" (mid-point of guage swing). The needle never budges from that spot. It's the same now that I'm back home; it's actually much hotter here in VA than it was in FL last week.

 

[Missouri Mule]

As long as it is not over heating you should be Ok.

But check your coolin system out anyway (especially coolant).

Fan clutch also. It mite be activating fan.

Mine floats but every now and then it will hang at 185.

 

[Nate]

When I was working in Alaska, we had about 15 CTDs, from 96 up to 01 and they ALL did that. Would hit 190* come down to ~160* or so, climb back up... back down.



So I don't think it's a problem. I mean I can imagine 15 trucks, different years, 12v and 24v all doing it and it not being ok.

 

[fortunate1]

I don't think that the fluctuation is a problem either. I just wanted to let everyone know that immediately after thoroughly cleaning the radiator (and the a/c, trans cooler, and intercooler) the needle quit swinging back & forth. The fan clutch works; it has come on a few times in this hot weather - never on for more than a minute or so.

 

[McCRam]

I think it is a problem. Sometimes mine fluctuates, most of the time it stays at 170*. This Problem started in April for me, and got worse. I added a new temp gauge to confirm the readings the factory gauge were giving me. I talked to a mechanic at rocky mountain cummins today about this problem. He is positive that water is getting by the thermostat one way or another. He told me to check the orings that seal the tstat. He also thought that maybe the jiggle valve in the head might be sticking. That is the fitting that the little hose attaches to on the cylinder head, right by the tstat. I didn't know that was there before today. He stated that valve will let 90 cc's go past the tstat. I am going to replace the jiggle valve before I go home in the morning, If that doesn't fix it, I will tear into the tstat AGAIN. Hopefully something works. I'll let you know what I find.

 

[McCRam]

The valve did not help the problem. I replaced the radiator cap, (easy parts first). Now both temperature gauges cycle normally every time I restart the engine, warm or cold. Then after a few minutes it settles in at 170 and sits there. I still need to check the tsat again, I haven't had a chance to get at that yet.