Electric fan // question...

[extension]

Why does the electric fan keep on running, on some cars, after the engine is turned off?

I want to install such a system on my car and I dont know whether to wire it like this or so that, when the engine is turned off, electrical power to the fan is cut off as well..

The stock car is equiped with a fan on the water pump..Which will be removed.

The thermostat which i`m going to buy closes the circuit at 86Degrees C.

[UncleBob]

are you saying you want the fan to run when the car is off? There really is no point in wiring it that way, although it does simplify the circuit, because that way you can take power directly off the battery. To wire it from the ignition switch, you have to find a reference line for the relay from somewhere.

I'd personally rather have the fan not run when the car is off.....there is no useful purpose for the fan running when there's no coolant flowing, no matter how hot it is.

[Mr Wiggl3s]

Im sure it prolly has something to do with extra voltage being used up. I think this is only for foreign cars right?

[curtis73]

Its simply a design choice. Allowing the fan to continue running simply continues to cool the water after the engine is shut off. Keep in mind that water is an excellent conductor of heat. It doesn't need the water pump to cool the rest of the water once its shut off. The water pump is only there to enhance cooling when you're pumping thousands of BTUs per minute into it. Once its off it will transfer its heat to the radiator just fine which is why some cars continue to run the fan. Remember, early Fords didn't have water pumps at all and they cooled well enough that they would often freeze in the winter while you were driving.

It was typically a foreign thing for a while. What would happen is they would run the coolant close to boiling. When you shut it off, the stopped water would be allowed to remain in motionless contact with the hot metal. Within a few minutes it could start to spontaneously boil. The fix was to keep the fans running if it was above a certain temperature. The cooler water in the radiator would sap enough of the heat from the rest of the water to prevent boiling.

Its only a necessity (or rather I should say a crutch fix) to run the fans after shutdown if boiling is a problem. Hot engines have great benefits, like healthier oil, better MPG, less metal wear, and fewer emissions. Cool engines make drivers feel better. Its actually better for the engine if it stays hot longer.

[extension]

@UncleBob = "when the engine is turned off, electrical power to the fan is cut off" - meaning turning off the fan when the engine is turned off.

I understand what you are saying, Curtis, but if my car is originally equipped with a fan on the water pump (spun by the engine) isn't it safe to assume that turning off the fan once the engine is turned off is ok?

[curtis73]

Absolutely. That's how its more commonly done.

The only case in which it wouldn't be sufficient (rare but possible) is in a situation where the new electric fan wouldn't be sufficient at cooling the engine properly and it allows the stopped water to boil after shutdown... but that is very rare.

99% of the people I've talked with use a switched source for their electric fan retrofit and they have no trouble. If it ends up not being sufficient for you, its as easy as re-sourcing power for the relay. Just switch the wire from a switched source to a hot source.