My T-stat acted up clamping the coolant flow. I removed the t-stat but kept the housing. I also have a bad coolant sensor. I ran it for about 20 miles on the way home with it running hot. It shut down twice and the restricted performance light came on. After removing the t-stat the restricted performance is off, the engine isn't running hot, but I want to know if this can cause permanent damage if not immeadiatly fixed. There is a rough idle and a slight grinding sound, like someone running two plates together. It runs fine, just noticeable at idle, and it is a bit noisy. This could be attributed to the previous owner using regular gas, I am trying to run it almost dry before I refill it with premium. I just don't want to unknowingly run it into the ground. Anything I should check? It is a 1999 XJR 69K.

 

ianann, yes, running the car with no thermostat in it can lead to overheating of the engine. What ends up happening is when you have the engine just idling, the flow is slow enough that normally the engine will run cold and you end up with the computer compensating, thinking that the engine needs help warming up. So, the computer runs the car slightly rich. When you get the engine RPMs up, the flow of coolant through the radiator also picks up. In this case, the coolant spends so little time in the radiator, that it can't be adequately cooled before it is sent back into the engine and heated even more. By adding the restriction of the thermostat in there, you slow the flow enough that adequate heat can be removed from the coolant while it is in the radiator.

 

Thermo,

I know you like to apply general knowledge to specific cases, and there's nothing wrong with that (or your efforts). Running an engine with no thermostat is not going to overheat it, not from my experience anyway. Not that it's a good idea, though...I addressed the other effects on engine performance in a reply to this guy's parallel thread, and you have that part right.

 

JTO is right. We get people who remove their tstats in an emergency and then drive them in, "just to get the car there". I've had no engine overheating issues experienced by me or in our shop because of missing thermostats.