Temperature rise a motor after shutdown
Temperature rise a motor after shutdown
(OP)
In a forum I'm a part of there were a couple of people saying it would be okay to drive without a radiator fan in traffic as long as you turn the engine off at each light to keep it from overheating. While I understand their intuitive thoughts on this I've known engines to actually spike in temperature a bit after being turned off. Even though you're not generating any more heat through combustion, you've also lost the forced convective cooling of the coolant system. Since the heat that has already been generated has no where to go it ends up increasing the core temperature of the motor itself. I've witnessed this both in a car that I had many years ago that I drove for awhile without a radiator fan and in an electric motor that I did tested with thermocouples under load.
I've been trying to find more data about (and perhaps a name for) this phenomenon and since I've been having difficulty finding any type of source I wanted to confirm I'm not crazy as well. :) Thanks for the help!
I've been trying to find more data about (and perhaps a name for) this phenomenon and since I've been having difficulty finding any type of source I wanted to confirm I'm not crazy as well. :) Thanks for the help!





RE: Temperature rise a motor after shutdown
There is no specific phrase which I know of but try googling things like "Thermal Lag", "Thermal Over-run", "Thermal Peaking". There are likely some industry-specific terms.
This phenomenon is why car radiator fans keep running for a few minutes in hot weather after a hard drive when you switch off , get out and walk away. They are designed to do it - I noticed French cars are very keen on doing this.
gwolf
RE: Temperature rise a motor after shutdown
If you turn the heater on in the passenger compartment that will usually prevent overheating of an idling engine.
RE: Temperature rise a motor after shutdown
For a water cooled engine to work the water temperature inside the block - at steady-state operating conditions - must be lower than the jacket temperature. It it wasn't there wouldn't be any heat transfer.
The water gets lower by passing through the water-to-air heat exchanger commonly referred to as a "radiator".
When you shut the engine off you also shut the water pump off.
Heat from the jacket still transfers into the water, but because the water is no longer circulating it can't reject the the heat, so it has to get hotter. The block meanwhile is getting cooler.
Eventually the water and block temperatures equillibrate, and the both will start to fall.
The total enthalpy in the engine/coolant system can only decrease after the the engine is shut down, but the temperatures of different parts of the system may increase.
RE: Temperature rise a motor after shutdown
I had a Honda with a faulty fan switch and I drove it around for quite a while before I realized it was broken because I don't idle my vehicles long.