Asadowsky1991

Hey guys, I have a 99 XJ 4.0L with about 114k miles on it. I just replaced the water pump and figured i would throw a new thermostat in there since the coolant was drained anyways. Jeep always ran at 210 degrees on the dot before the pump and T-stat replacement (WP was starting to squeak so i figured it was on its way out so i replaced it). Now with the new pump and T-stat my temp runs about 185-205 degrees and usually fluctuates between those temps as i drive. It never holds steady at 210 anymore, if it gets to 210 then it immediately drops back down to 190 ish. I used an OEM replacement Thermostat that was rated at 195 degrees, not so "low temp" BS. My heat works great and comes out hot within seconds of turning it on. Only thing i noticed was that my radiator "drank" about a half of the overflow tank after the new change. Could I have just underfilled the actual radiator when i did the change and now it is pulling from the overflow to get it up to capacity? I open the radiator cap and it is at the top, almost overflowing out.

Is my cooling system just being super efficient now that it has new parts and fresh coolant? Or is it bad that it does not stay right at 210 anymore?

MagicMexican

Did you buy one of those 'fail-safe' thermostats? Those are particularly touchy, and will lock themselves open prematurely, and then you'll get those symptoms.

Asadowsky1991

Replaced it with a Stant 45359 SuperStat Thermostat. is this what you're talking about?

MagicMexican

No, it would look like this with the little mechanism on the side.




But I just googled your part number, 45359 is a 195 degree thermostat...
https://www.amazon.com/Stant-45359-S.../dp/B000C7YRNM

that plus some air in your system could explain the fluctuation.

kgm

That's seemingly how mine works. The t-stat regulates the temp, it will be more noticeable in the winter due to the temperature.

freeworld71

I just did the same maintenance to my jeep. Could be the winter temp but I noticed the engine temp goes up when idling at a light or something. When I take off and drive the temp goes back down below 210. I read somewhere that that was normal for it to heat up like that....I'm not sure about the low temp. Makes sense that it would hang around 195.

CurrySoSpicy

Let me share my experience as well, I performed a cooling system rebuild as well. Water pump, t-stat (195), radiator hoses, radiator (replaced a year ago), water pump inlet tube, new coolant. My XJ heats up to just a hair under the 210 mark and varies within the 210 mark and the mark below.

Asadowsky1991

That's exactly everything i just replaced, minus a new radiator. The way you describe the temp sounds exactly how mine is running now. Glad to know its all normal. Thanks

CurrySoSpicy

Let's keep in contact, let's see how they run in the summer and touch base, if I remember I'll send you PM once it gets hot out. We can compare notes. 👍

cruiser54

Only use the factory stat from the dealer.

BlueRidgeMark

I just replaced mine, and I'm seeing the same. More fluctuation than I used to have.

Newer breed of thermostats operating differently?

cruiser54

WunHungLo and his comrades think they're good enough to sell to us.

I INSTALLED 6 SUPEERSTATS IN 3 jEEPS AND NEVER GOT ONE THAT WOULD COME UP TO TEMP.

Switched to Mopar and all is fine in winter and summer.

CurrySoSpicy

I have a mopar t-stat in my rig

cruiser54

Take it back.

CurrySoSpicy

huh? I though mopar is the one to have?