I just redid the cooling system on my 90 i was wondering if its bad to leave out the theromstate out because after i was done i realized i forgot to put it in. Its cooling great now i just want to know if its a big deal to leave it out

 

unless you like 5mpg, put it back in.
They need to run at 190-200*

 

FSM ('98) says "do not operate without a t-stat" and "a warm-up cycle is counted when the ECT sensor has crossed 160F".

 

Yes, it's bad to leave it out, the truck wont warm up right, and it wont run right. It only takes a couple minutes to pull the housing and throw it back in there. I tried running even a 180 t-stat and it wouldn't get warm. So I swapped it back out for a 192 t-stat and it still runs a bit cool. New billet water pump, and new aluminum radiator made a huge difference haha.

I will swap the 180 back in this summer. They are designed to run a stat.

 

Yes...

 

I always thought an engine might overheat without a thermostat.

The idea of temp control requires that water remain in the radiator to cool down, the thermostat acts as a timer sort of. It holds the water back until it reaches a certain point, once that point is reached it opens up allowing heated water to flow into the radiator while cooled water is pulled into the motor. Once the water in the motor cools to a set point the t-stat closes and allows the cycle to restart.

If you remove a the t-stat the water flows constantly through the radiator, never having a cool down cycle.

While the water will probably cool down too much in the winter, you run without that t-stat in the summer and you will see overheating.

I know I had a truck when I was in Texas it was overheating a lot. The thought was relayed to me that the t-stat was either not opening or it was not closing. So I went to pull the t-stat and it was not there.

I installed one and the overheating stopped.

I guess the effect of not having a t-stat depends on the ambient air temps.

 

If coolant stays in the radiator longer (cooling), then it's also staying in the engine/head longer (heating). Coolant flowing thru the rad too fast is a myth. Again, the t-stat does one thing and one thing only, controls MINIMUM coolant temp. Ambient temp, especially the warmer months, plays a big part in the XJs max temps, mainly due to the dinky rad surface area.

 

If the car is computer controlled, Yes... If we're talking old school stuff with a carb and no O2 sensor, then leave it out of you want, nothing bad will happen.

 

No good reason to run without one. Doesn't take long to install.

Use a 195 degree thermostat, and don't buy a cheap one. I get mine from Jeep and also like the Stant SuperStat.

 

thanks everyone ill put a new on in today

 

Lol djb, I've seen you put this down in so many threads. Might just be easier to put it in your signature, along with the backpressure myth.

 

The newbie OP possibly didn't know it. Does me posting that info upset u? U disagree?????????? Thanks for putting it in big, bold, italics.....u da man.

 

No no no, I don't disagree. Lol if anything, I agree 100%. I was just saying that I've seen in many different threads where you've had to mention this, and I was just joking when I said to put it in your sig. No disrespect intended. I apologize.

 

No, no, no.....my bad......been working on income taxes....argh, grrrrr.

 

Income taxes? What is that? I thought you could offset income tax liability with money spent on XJ repair.................??