2000 TJ running without a thermostat?

[PlexusTJ]

Hi All,

I have been doing to normal servicing items on my Jeep and came across the strangest thing, my Jeep has been running without a thermostat.

As you can see in the photo, the previous owner (or mechanic) went to town on the gasket sealant they used (there was no gasket, just the sealant) and there was no thermostat, which I’ve never seen.

Are the any reasons why someone would do that? And more importantly, would it cause any major issues I should be aware of?

 

[NskLJ]

Removing a thermostat could have been a trail repair for a stuck thermostat or it was something people used to due on older vehicles to make them run cooler. Vehicles need the thermostat to regulate the temperature in the engine and allow the coolant enough time in the radiator to cool. I would install a new thermostat and gasket, flush it now if needed with the thermostat out if needed. Put it back together with the 195 degree thermostat called for and drive it while monitoring the temperature to see if you have anything else going on.

 

[PlexusTJ]

I’ve had the Jeep now for about 6 months and to be honest, I’ve never seen the temp gauge change at all, always go up and stays in the same place, which worries me a little knowing the thermostat wasn’t there.

But interesting to hear about the trail repair, I don’t know the history of the car so you could be right.

I’ve got a new thermostat and housing so I’m going to replace both and flush like you say.

 

[macleanflood]

New housing are never straight...you'll need to sand it out on a flat surface.

More work you put into cleaning the block face and housing the better luck you'll have with the seal.

I've never gotten a leak free seal with a gasket...last couple times I didn't bother and just used Right Stuff.

-Mac

 

[KennethS]

No thermostat may cause increased fuel consumption. IF the coolant temperature is below nominal, the ECU would think the engine is still warming up and run it a bit richer.

I ran mine with no thermostat while flushing the radiator, and it was very obvious the temp gauge was much cooler than normal. As in below the first line on the left which I think is around 150 degrees. I estimated the coolant temp was around 130 with no thermostat.

If your temp gauge was indicating normal with no thermostat (around 200) then there‘s an issue with the cooling system.

 

[Jerry Bransford]

Go with a conventional type 195 degree thermostat, avoid so-called "fail-safe" thermostats which actually are commonly known to fail in the open position. Install it so its air bleed vent hole is positioned at the top to allow the cooling system to bleed itself of trapped air. If there's no vent hole on the flange drill one.