watercooled engine question

[Planter91C2]

in a watercooled engine, when you turn the engine off, does it get hotter for a bit because the water flow cooling system has stopped, or does it immediately begin to cool down?

[rcecale]

I've always heard that to be the case, but I've never really kept track of it on any vehicles I own. I does make sense, however that it would, since it is the flow of water through the cooling fins of the radiator that brings the 'cooling' effect to the rest of the engine...once the flow is stopped and the water is no longer being cooled, the hot surfaces it had been cooling would tend to raise the temperature somewhat.

Randy

[Obin Robinson]

Originally posted by Planter91C2
in a watercooled engine, when you turn the engine off, does it get hotter for a bit because the water flow cooling system has stopped, or does it immediately begin to cool down?

the water pump stops circulating water, but as long as the thermostat is open the hot water is being exchanged with cooler water somewhat. so yeah, the engine gets a little hotter for a minute or so, but then the engine cools down after that.

because engines are different, some cars heat up a bit more than others after shutting them off. turbo engines, for example, will heat up a bit more than NA engines if you shut them off. this can even damage the turbo. newer engines don't have this problem however.

obin

[island911]

"does it get hotter for a bit " No.

The total heat energy of the engine does not increase, once shut down. The water, local to the head, (maybe even external surfaces) may see a temp rise, (compared to when pumping) but the engine has not increased in overall temp.

edit: . . . it's a "transient heat" thang.

[Obin Robinson]

Originally posted by island911
"does it get hotter for a bit " No.

The total heat energy of the engine does not increase, once shut down. The water, local to the head, (maybe even external surfaces) may see a temp rise, (compared to when pumping) but the engine has not increased in overall temp.

edit: . . . it's a "transient heat" thang.

right. the only thing getting "hotter" is the head and the coolant temp sensor. but you're correct, it's not like the engine is acting as a heat sink.

the only thing i know that gets hotter is the cast iron manifold will transfer some heat into the aluminum heads after the car is shut off. but in turn, the manifold gets cooler so the overall heat does not go "up" so to speak. the existing heat just goes to a different place and that place is usually close to where the temperature sensor is.

obin