What Causes A Thermostat Housing To Crack



My engine light came on and I took my 2016 Jeep Cherokee latitude in and it is still under 36000. This was just after a hard freeze and I purchased and had the vehicle less then a week. They kept it 2 weeks and then the repaired it saying it was just a simple mechanical malfunction of the thermostat housing. What would cause such a malfunction?

The T housing was actually cracked and the base (where it mounts to the head) didn't have a gasket. So I have all the parts on order and hopefully this will solve my coolant leak during warm up idle! New issues.I went against the old advice 'never stick your hands where you wouldn't stick your face' and felt the inside of the head. I was replacing the thermostat in my '06 Saab 9-3 2.0T today and when I was reinstalling the housing, the corner of the housing cracked. I know this operates in a high pressure and hot environment, but is there a way to fix the crack? Prices and shipping time for a new one are tough to.

  1. Over tightening causes leaks. The housing uses the seal on the T-Stat to provide a seal to the water pump housing. I'd drain the coolant and check the seal on the t-stat, and the housing to see if it's warped. Could be that the t-stat housing was over torqued 2 years ago, and warped it.
  2. If a vehicle is overheating, a bad thermostat could be the problem, and a damaged thermostat housing is more likely to produce a coolant leak, either from a cracked or warped housing or a failed seal to the engine. The thermostat housing can be made of metal or plastic. Also, can a leaking thermostat housing cause overheating?

My car has 32000 miles.
My car has an automatic transmission.

Marvin Sunderland
22 years of experience

Hi there. If the thermostat housing was made of plastic (carbon fiber) and the temperature outside dropped below the freezing point of the cooling system, then the coolant would have froze up and expanded causing the thermostat housing to crack. Also, if the coolant has too much electrolyte causing a slight voltage in the coolant, then the chemical compound will break down causing the cooling system to eat up seals and carbon fiber.

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