Originally Posted by fmugur

I just though of this option since lately I have been using the REST to keep the car warm for a bit after I turn the engine off.
I know some bmw models or other cars have the fan running after the engine is turned off in hot days but I didn't see the reason if the water is not moved through the engine.
I know for a pool heater for example the same thing is recommended and I have done some damage on my heater because I used a timer on the pump although the heater shuts off when no water flow. The pool heater manufacturer recommends to run the pump for a few minutes after the heater is turned off.

The idea is that the burner, in car case the cilinders, build up heat and if nothing is taking the heat away from the fire that just stopped, the temperature goes higher than 108C for a short period of time. How high I don't know but I guess we can measure it. I did see it going up on the pool heater but that system is not pressurized and the temp sensor is right there.