Thermostat woes w/o complete failure

[benrk]

Hi,

This is not a question, I have things figured out now & am reporting my findings as I had not experienced this before nor read about it anywhere.

I usually know bad thermostats to completely fail & get stuck fully open or fully closed.
Engine warm up time & coolant gauge readings didn't give me any reason to question thermostat function. However, in severe cold cabin heat was not what I would expect from a car designed by people living in subarctic climate.
As a remedy I flushed heater core & cooling system with only little improvement.
Next I started monitoring actual coolant temperature with an ELM dongle & the torque pro app: it went up to 81C & then dropped again to remain in the upper 70s. As there are aftermarket thermostats available with opening temp's as low as 82C (for dessert operation?) I assumed that's what a PO had put in the car & got an oem 91C unit. To my surprise oe 91C was exactly what I found in the car.
Now with the new thermostat coolant goes up to 91 & then stays in upper 80s. Engine warm up time has not changed, but cabin warm up time & heat output has much improved.


Hope this helps someone, greetz, Ben