Engine/Transmission (1998.5 - 2002) 190 deg. thermostat failure

[ERuhl]

Back in September my truck started running hot towing on the big hills when it never used to. At the time I was convinced the radiator was clogged due to the crankcase vent bottle at the front of the motor and sure enough it was, so I removed it and cleaned the radiator. No doubt that contributed to it, however after swapping out the thermostat this weekend I believe I finally found the real culprit (see attachment).



The thermostat part number is 3946848, the same part number as the 190 deg thermostat I bought to replace it. My camera doesn't have macro mode, but in the attached pic you can see (barely) the spring and washer separated from the bottom of the thermostat. This left the washer permanently blocking the coolant port, and when I removed the thermostat the spring and washer stayed behind. There used to be a small snap ring that kept the assembly together, but who knows where that is now. With the new thermostat in place I shouldn't have any cooling problems this summer. The old thermostat used to bounce between ~175 degrees and 190 degrees while driving which annoyed me and prompted its replacement this weekend. So far the new one seems to do a better job of holding a steady temperature.



At ~$70 for one of these thermostats I sure wasn't expecting to find the old one in pieces!

 

[Duluth Diesel]

Good info! My '02 has been doing the same temp fluctuations, and I don't like it. It has also gotten pretty warm while pulling up bigger hills. Sounds like I may have the same exact problem.



-Chuck

 

[ERuhl]

Sounds like I may have the same exact problem.



-Chuck

Check your radiator as well, the crankcase vent bottle makes a mess of it. Here's mine after ~80k miles and I drained the bottle at every oil change (5k mile intervals).

#ad




After cleaning the radiator I removed the bottle and extended the hose to behind the front axle.

 

[KBrasch]

I have had high temp problems in the past and just checked the TSB's for my truck and there is a revised P/N of 05015090AA listed for it. Haven't checked into it at DC yet but that could be our problem.