Engine/Transmission (1998.5 - 2002) HELP - is my new t-stat bad???

[zman]

Hey guys,



I have put in two new 180* thermostats in the last two weeks and both of them cause my truck to have 15* swings in coolant temps. Anyone know what's wrong? I can't imagine that both t-stats are bad, but maybe they are. Coolant temps cycle between 180* and about 165*. The t-stat part number is 3954194. My old 190* never did this. Any ideas?? Thanks guys!



Steve

 

[Whitmore]

zman

I have read that our trucks only use about 20 to 30 % of the cooling system while not towing so I think what you are seeing is that when the t-stat opens it lets cooler fluid in and then your motor temps drop, I wouldnt worry about it if I were you. I have witnessed this myself for the first 10 to 15 miles of a winter trip.



cheers, Kevin

 

[LSMITH]

Steve, long time no talk.



I put in the new 180 as well when I changed my coolant and got the same results, at least 15* swings. The old style thermostat that came in my truck went up to 190, dropped to 170, up to 180 and never moved. This new one swings until I shut it off no matter what the conditions. Nature of the beast with the new style thermostats.

 

[EricBu12]

Steve,

Both T-stats were ok, the coolant has 6 gals in it so when it is cooler out, the swing is longer especialy at idle.



I make a winter guard that fits in the openings of the grille to restrict the airflow to keep the coolant at a more moderate temp. Also to help it warm up faster.

Here is the link to the classified ad for them



https://www.turbodieselregister.com...display_db_button=on&db_id=21&query=retrieval



E-mail me if you'd like a set

Eric

 

[zman]

hmmmm....

I would agree that both of the 180* t-stats are probably good, but why didn't the original 190* t-stat act like that? Seems like I read somewhere that the new 190* t-stats are 2 stage - they open up partially under no load and fully under a load (higher coolant temps) in order to maintain a steady coolant temperature. Anyone else remember seeing this somewhere?



Steve