I took apart my thermostat housing to find this...

The thermostat was bent and pushed up off of the seat. The car has been running fine and has never shown any signs of overheating. This is a track car in which I am running a Rebello L30 with blocked heater circuit, aluminium 3 core rad and a 20psi cap.

Has anyone ever seen this sort of thing before? I don't want to just throw a new thermostat in there if this is a symptom of something else being wrong with the cooling system.

Thanks

Have you dropped it in boiling water to see if it works, if it opens? If it is a bad unit and failed to open then...but it would take a lot more than 20lbs to push the lip up. Interesting problem.

Steve.....Did you wind it up before the thermostat opened? I blew a freeze plug once by revving 7000 before the thermostat had opened.......that pressure could bend a thermostat if you have too many revs with no exit.

The thermostat opens as it should around 160°F in a pot of water. I have always tried to keep the RPMs down until the car is fully warmed up but I can't say for sure that I have done so 100% of the time.

Check for intermittent compressed air or exhaust from the chambers getting into the coolant system when the block is cold to be safe.

Thanks blue. What's the best way to do that sort of test? Check for bubbles?

I only saw it once. When the rad cap was off and the car started, the pressure blew water out of the rad filler hole like a volcano.

There are pressure gauges for coolant systems that you can use. Just fit one on with the motor cold then run until warm. Rev it occasionally during the warm up period to see if the pressure changes much while reving.

Merry Christmas!

That makes sense Blue, but why would it just compress your water jackets when it was cold? I'm sure a blown head gasket could exert that amount of pressure in the right place, but why only when the engine is cold. I assume your engine is running OK Steve....right? Do you believe a water pump could exert enough pressure to damage a thermostat or freeze plug if it backs up enough pressure behind a closed thermostat or is that probably not possible?

The car runs great. No issues. I would not have noticed the thermostat if I hadn't have removed the top rad hose and looked down the pipe into the thermostat housing. I will try to get my hands on a pressure tester and do some more investigation.

Hmmm giving it more thought. Is it possible that one of the sensors could have been installed after the thermostat and the sensor pushed sideways on one of the thermostat side towers?

Good thought Blue but there is only one sensor in the thermostat housing and it does not contact the thermostat regardless of how I clock it.

I am reading this with interest as I have a very similar setup: Rebello 3.0, aluminum 4 for radiator (heater core is not blocked off) and I have a 13 PSI cap. I had mine apart last summer and it looked fine. Are you running a diesel water pump?