Engine/Transmission (1998.5 - 2002) Low Water Temperature - Thermostat?

[HeavyHauler]

Hey fellas. In the past I've had no problems with flunctuating water temps but yesterday might truck warmed up to the usual 190 mark (or very close) but then I noticed that it dropped to about 170 after I had driven it for about an hour an a half.



I cut the truck off shortly after that and then it only warmed up to 165 and stayed there until I turned the truck off after 80 miles of solid interstate driving.



I did have my cab temp set pretty low and the outside temperature was probably 40*. I read somewhere that this is normal if you are keeping your cab temp low with low outside temperatures.



I just drained and refilled the radiator with coolant but didn't think about changing the thermostat.



Do I need to change it now? Do I need a 180 or 190?



Also, am I gonna have to drain my coolant again to install the new thermostat?



Thanks for the help!

 

[rblomquist]

I just changed out my 2nd themostat in 2 years on mine. The one I bought this week was a completely different design than the last 2 I bought; hopefully this one will be more stout. These t-stats have a history of going cold prematurely. One of my neighbors is a maintenance guy for the local refuse company and he said almost all the garbage trucks have cummins engines in them and they too have to replace t-stats a lot.



I'm going to say your truck probably requires the 190, my 99 takes the 180 though. The good news is that you won't find an easier truck to change the t-stat You don't need to dump the fluid, I only lost between a quart/quart and a half. Unscrew the 4 bolts, take out the old t-stat, pop the new one in (no gasket needed), tighten it down, then top off the fluid. After you drive it next time and it cools back down just see if you need to top off the catch tank a little and that's it!



It took me all of 10 minutes to change mine out this time and that included popping the hood, getting the socket, and putting the stuff away... . you gotta love that.

 

[HeavyHauler]

10-4! I'll give Cummins a call tomorrow and check on some prices. Napa Online gives a price of $29. 99 for the stat and seal, and it's also a 190. I think I'd rather get a Cummins part though if possible.

 

[rblomquist]

The Cummins one I just bought was under $30. I've never had one physically break on me, just got weak and not wanted to stay closed. I suppose if you have to have a bad trait in a t-stat the trend on these wanting to stay open more often is better than having a different brank going to the stuck closed state.

 

[bighornram]

My truck has not ever had a stable temp. guage!!! I traded off my 2000 shortbox for an 02' long. The 2K had a guage like a rock, rising steadily to it's operating spot and then never moving up or down. This '02 rises above it's operating temp. location, then drops a good 1/4" and warms back up to operating level. Even then it fluctuates. Just thought it was something with this truck. Guess I will change the thermostat. Maybe it was a bad one from the start.

 

[rkressg]

I went through 3-4 t-stats before I found one that was steady. My temp would always jump around, but the most recent one I installed fixed that problem.

 

[magaliasram]

Just a quick note, I just replaced my Thermostat with one from the NAPA store. The cost was 25. 39 with the tax. I was having a problem with my truck not heating up. After some reading on here and a teardown of the t-stat housing and removal of the t-stat I found the problem. The t-stat acted like it was sticking in the open position. After inspecting it I found it was actually closed but that the rubber seal around the t-stat valve itself had deteriorated and would not allow the valve to close all the way. I actually think that the valve was closed as far as it could go but that with part of the seal missing it left a gap for water to bypass the T-stat. After replacing the t-stat I now have a normal operating temp again. I run constant one needle width below the 190 mark. I will not wait for this to happen again from now on I replace the t-stat at the same time I pull the radiator to clean the fins. (every two years) The coolant has always looked fresh. So now I have added my 2cents worth.