Replacing thermostat - Questions

AkXb70 · May 7, 2025

This weekend, while driving I noticed my coolant temp fluctuating fairly quickly and repeatedly (running up to 212, then dropping to 199, then repeating within a minute). From some past threads, it looks like a bad thermostat was the issue.

Questions:
1. I ordered a new thermostat, but it did not come with a gasket for the housing. Do I need to source a new one or is it an O-ring or something on the housing side?
2. Do we have a drain on the rad that I can use to lower the coolant level before popping the housing off and dousing everything?
3. From a cursory glance, one of the bolts seems to go through the housing from the front? Will I need any special sealant?

Jrlottjr · May 7, 2025

I just replaced mine last week.
1. There should be a rubber seal around the disc of the new thermostat. It fits in a machined relief and seals the assembly.
2. I did not drain ant coolant and had minimal loss. The reservoir dropped maybe a half inch.
3. You will need to bleed the air from the water pump after re-assembly. There is a bleeder plug on top of the water pump that needs a 5mm Allen wrench to loosen. With engine off, loosen the plug and let the air escape, then tighten the plug.
4. No sealant is necessary.
I installed a 192 degree thermostat and it runs between 109 and 194 degrees now.

AkXb70 · May 7, 2025

Thanks! I did get the 192* tstat from MMX, but mine does NOT have a rubber seal...so I guess I'm missing that.

JJ'sTRX · May 9, 2025

Jrlottjr said:
I just replaced mine last week.
1. There should be a rubber seal around the disc of the new thermostat. It fits in a machined relief and seals the assembly.
2. I did not drain ant coolant and had minimal loss. The reservoir dropped maybe a half inch.
3. You will need to bleed the air from the water pump after re-assembly. There is a bleeder plug on top of the water pump that needs a 5mm Allen wrench to loosen. With engine off, loosen the plug and let the air escape, then tighten the plug.
4. No sealant is necessary.
I installed a 192 degree thermostat and it runs between 109 and 194 degrees now.

Thanks for the detail! I was wondering how much coolant loss there is when removing the housing. About how much coolant did you add to bleed the system? I keep an extra stat in the truck just in case, but need to keep some coolant in there as well.

916Ghost · May 10, 2025

Do you need to retune for the 192 degree stat or it work ok and no codes?

AkXb70 · May 10, 2025

I read that the 192 doesn't require a tune, which is why I went with it. Hoping to install it as soon as I get a seal. I don't expect a code with how warm it is here.

Jrlottjr · Monday at 1:32 PM

JJ'sTRX said:
Thanks for the detail! I was wondering how much coolant loss there is when removing the housing. About how much coolant did you add to bleed the system? I keep an extra stat in the truck just in case, but need to keep some coolant in there as well.

My coolant level was at the maximum level and it hasn’t dropped below minimum, so I didn’t add any. When you remove the air bleed, air will come out and a stream of coolant will follow. I kept the plug close to the hole with an extension and plugged it back when no more air was present. No codes have been generated. I’m sorry for the typo but my temperature is running between 188 and 194.

Jrlottjr · Monday at 1:37 PM

916Ghost said:
Do you need to retune for the 192 degree stat or it work ok and no codes?

I haven’t had any codes.

JKMTRX · Monday at 3:54 PM

Jrlottjr said:
I haven’t had any codes.

192 you should be fine on stock tune. 180 deg thermostat will throw a code without tune.

AkXb70 · Tuesday at 9:13 AM

Finally got my rubber seal in.

Just to verify for the bleed process, after swapping the new thermostat, run the engine up to operating temp, adding coolant as necessary, then shut the engine off, back out the air bleed until coolant dribbles out, reinstall everything including the intake and good to go?

RedEyeTRX · Tuesday at 12:57 PM

AkXb70 said:
Finally got my rubber seal in.

Just to verify for the bleed process, after swapping the new thermostat, run the engine up to operating temp, adding coolant as necessary, then shut the engine off, back out the air bleed until coolant dribbles out, reinstall everything including the intake and good to go

Pretty sure you want the engine cool, before opening the bleeder valve. Otherwise its under pressure and you will be wearing the coolant.
@PotterTRX should know the procedure.

AkXb70 · Tuesday at 1:02 PM

Whoops, I loosened it at temp, but kept the plug in, engine off. Only fizzed a little. Seems to be working well (max 194/195*), but I'll take it for a longer drive after work to make sure.

RedEyeTRX · Tuesday at 1:05 PM

AkXb70 said:
Whoops, I loosened it at temp, but kept the plug in, engine off. Only fizzed a little. Seems to be working well (max 194/195*), but I'll take it for a longer drive after work to make sure.

If and when I have to do mine. I would bleed it cold, then start the truck with the radiator cap off (so it doesnt build pressure). Then bleed it again. After driving a few hundred miles, bleed it one more time.
But that is just me. Cheers !