My dad's '02 H.O's temp is fluctuating quite a bit. It goes way over to nearly 205-210* when the stat initially opens and will fluctuate between 190-205* depending on throttle input. Pulling Donner pass EMPTY at 70mph in 60* weather let it get to 205* or so, cooled right back to 190* as soon as we crested and headed down the back side. 100K on the truck almost exactly. Radiator is mildly dirty from blow by but not near as bad as my '01 was and don't think it's dirty enough to make that much temp. fluctuation. Thermostat or Fan clutch? It doesn't usually chirp the belt either, not like my '01 does.
Change the T-stat with a new Cummins part and give that a shot. Some of the aftermarket T-stats do what you've explained. Plus a thermostat is a cheap process of elimination. Can you hear the clutch fan come on when the temps rise?
Mine does that exact same thing and always has since it was new . My fan clutch works as designed and very well at that. There is no doubt when it it engages - sounds like a freight train coming down the tracks . I have close to 85,000 on the odometer now and all is well. I do plan on replacing the thermostat soon as part of preventive maintainance but not beacuse of the temp fluctuation. Tom
Hmmm..I called my local dealership service department and they would guess a thermostat. He said most of the diesels that come in with a temp problem is from a clogged radiator or a tstat. THe dealer has Cummins tstats right? I'm going to get one in a minute, change it, and also remove the radiator and clean out the fins while I'm at it. Tom, You mention your temp fluctuates too....is this a High Output thing? My '01 SO goes a little over 190* as the stat opens and then returns and stays at 190*, unless I am pulling something uphill.
I never really noticed other CTD trucks and what the temp gauge did , or did not do , so I asked a couple of fella's that have S/O trucks today and they said that their gauges do not fluctuate as much as mine does. The only other folks that I know around these parts with H.O. motors are 2003 and newer trucks - I can not compare notes with another 2nd Gen. H.O. owner. All I can tell ya is that mine has done it since day one . Keep us posted on how your dad's truck reacts to a new T/S. I would assume that the Dodge piece is a Cummins part but I do not know for sure...... Tom
Installed a new tstat, and removed the radiator for a thurough steam cleaning. The Dodge stat is indeed a Cummins part, but at $50. I also noticed that the new tstat was considerably larger than the original piece. The mouth was larger in diameter and it had no bipass holes like the original. My guess would be to promote quicker warm ups and more flow under heavy load. The new larger tstat and clean radiator seems to make a big difference. I only put about 3 miles or so on the truck this afternoon just for a test drive but found the temp to rise just a hair past 190* and drop down to about 165* or so in a matter of a few seconds. That must definantly be a larger tstat. The truck continued to climb to 190* and drop way down, less on the second and third cycle. I would imagine if I had traveled a few more miles the temp would had stabilized at 190*. All in all, huge improvement. I plan on going with a new tstat in my '01 3/4T For the added flow.
