Engine/Transmission (1998.5 - 2002) Fluctuating engine temperature, normal???

[Tomscreek]

I just noticed today while driving home that the temp guage would go up and down about 10 degrees, 190 then drop to about 180 (as best I could estimate from the guage) then return to 190. I don't remember ever noticing this before. It was pretty chilly outside about 39 degrees cruising about 65 mph. Is this normal or signs of faulty thermostat?

 

[JLandry]

Mine does this to some degree (no pun intended), but I don't think it's that much. I'll bet the cold was the reason for the large derivations you saw. If it gets worse, it probably couldn't hurt to replace the thermostat and make sure the radiator fins are clean and open.



EDIT: I drove my truck to work this morning and paid more attention to the coolant temperature due to this thread. I have a ScanGauge installed which can display the coolant temp as reported by the ECM through the OBDII port. The outside air temp was about 55 degrees F and the coolant temp was about 80 degrees when I left the house.



After about a mile of driving on side streets, I hit the freeway at 60 mph. During the next 10 miles of steady cruising, the coolant temp gradually rose to 193 degrees, and then within a couple of minutes it had smoothly dropped back to about 181 degrees. Then it rose back up to 191 degrees, then back to 183 degrees, etc, etc. These temp swings got smaller and smaller until the coolant temp stabilized in a range from about 184 to 186 degrees for the next 30 miles.



When I exited the freeway and stopped at an intersection to wait for a light, the coolant temp dropped back to 181 degrees before recovering to about 186 degrees.



Sooooo... all this just goes to show that some hunting of the coolant temp is completely normal as the thermostat reacts and adjusts its opening. I should add that my truck still has the original factory thermostat.



John L.

 

[mberry]

Completely normal and the swings will be slightly more as the weather gets colder. Keep your 190 degree thermostat in there during winter or you're likely to complain about not enough heat in the cab. I learned from experience in my '02.

 

[Tomscreek]

Thanks guys!!