Engine overheating

[MANDOBLE]

I've tested this effect several times in 109s and 190s.
You overheat the engine (neddle marking red zone limit), then stop the engine and, while gliding, in few seconds the neddle will mark a normal temperature again (below first yellow mark). At this point you start the engine at iddle and ... ...the neddle marks the red zone limit again.

Is this correct?

[715]

Sure.  When you shut the engine off it still has stored heat (i.e. its hot) but it is no longer generating new heat (i.e. its not combusting in the cylinders).  When you turn it back on the added heat load from combustion adds to the stored heat and makes the net temperature go above the limit again.

By the way- in AH you don't have to worry about engine heat at all.  The WEP turns off automatically when the engine overheats and you can still run at full military power in that condition with no ill effects.  You might say that this is not realistic, but prior online flight sims I have flown implemented a more realistic engine temperature modeling where over use of WEP would actually burn out your engine.  It was quite unpopular and was recinded rapidly.

715

[Jimdandy]

It over heats. You shut it off. A water cooled engine relies on the circulation of water through the engine to transfer the heat. The radiator relies on the circulation of the fluid to transfer heat. The air is still moving though the radiator but the coolant isn't moving in the block. Thus your only cooling the water in the radiator. The water in the block is heating. The heat in the engine takes quite a while to dissipate. Just go feel the hood of your car after a long drive. You can watch this happen in your car. In the summer it is worse. Get it hot and shut it off with the key in the ACC position. You will actually see the temperature rise for a while after the car is shut off. It can even over heat and pop the cap. Another example is in the winter time when you start your car when it's real cold. Watch your temp gauge if you have one. It takes a while for the heat to transfer out of the coolant immediately around the engine. You can watch the temp gauge rise to beyond your normal operation temperature. Then the water in the radiator finally gets warm enough to pop the thermostat and start the coolant flowing. You will see your gauge drop rapidly to normal temperature. It just takes a little it for the heat to transfer. In the air cooled engines the oil is much more important in the cooling of the engine than in a water cooled engine. In air cooled engines there is always an oil cooler. Look at a VW. If you shut off the engine the oil stop circulating. This causes the temperature to rise for a while. Also depending on the electrical system if you shut off the engine you shut off the power to the gauge. This is a very simple explanation with out going into heat transfer equation on you. I think you get the picture.

[Dingy]

I think what hes trying to ask is why doesnt the needle GRADUALLY return to the white area once its in the red when the engine is shut off?  The loss of heat when the engine is turned off isnt that sudden that the thermometer suddenly goes from red to white.

I've wondered about this as well.

-Ding

[Pepino]

With respect to the needle thing, If you shut down the engine, all needles needing electrical input should go to zero, as you cut energy.

With regards to the temperature, if you shut down an overheated engine, you severely risk permanent damage. If you stop the engine, the water pump stops working. Then, as the water is not moving, and the chambers are still very hot, it starts boiling. Water steam does not cool anymore so, if you are lucky, you cook the block joint, if you are not, you bent the head, maybe the block itself. You could limp home, but you would be leaking water and cylinder compression. Thus, less performance and, eventually, a dead engine.

The right way to cool an engine is to iddle it. NEVER stop it. You should cook your block joint (at least) if you stop an overheated engine.

Cheers,

Pepe