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[larso]

Alright...so the 931 that I drive is perfect only when cruising on the highway...engine temp nice, roof open...But once I go to park it in the grocery store parking lot, or in the garage...the head temperature heats up like crazy. Is this bad? Or is a hot head while parked not something to worry about?

I idle the car for about 1.5 minutes before I park it...but If I stay there and watch the temperature gauge in the parking lot, the temperature creeps up to the red. This is only when the engine is off, so the head is getting really hot. As soon as I turn the engine on, about 4 seconds later the temp needle drops down to the middle again (nice and cool). So are these hot head temperatures something to worry about if the engine isn't running? The rad fans come on while it's parked once in a while...but they just cool the rad, they don't cool the head temperature very much at all.

I guess what I am asking is should it be a concern, and do all of you notice this, or is there something odd wrong with my car.

The car does not go into the red while driving anytime. And no there are no gurgling sounds...And no I do not have an improperly bled system. Again, the car is wonderful at highway speeds, or even 45MPH. The head gasket/cylinder head can't blow or be harmed while the car is off can it?? i'm just afraid that if it's in the red zone while parked, when I go to start it up it might blow something...since the hot coolant is trapped in there.

[924 turbo]

Probably nothing to worry about. Since the temperature sender is at a very high point in the system, it will read very hot as soon as you turn the engine off.

This is normal behavior. Since the coolant is no longer circulating, and heat rises, and the sender is about as high as it can be, it reads very hot. As you said, once you turn the car on the temperature comes down to a reasonable level very quickly. Mostly, it's just a function of where the sender is located. If it were low in the system, it would read low when you turned the car off.

Either way, both of my cars do it.

[Smoothie]

I concur. It's called heat soak (which doesn't just affect electrical parts) and while not great, it's normal. Like Jon said, when the engine is shut off, all of the cooling functions stop (except for the fan blowing lightly on the radiator) so there's suddenly nothing to dissepate the heat and the temp first shoots up before it starts to cool down. It can become a serious problem if the car is already overheating while running. In that case, you're starting out with too much heat, so if you shut it off the heat soak will be more severe. That's why if you're overheating, it's better to leave the car running and slowly add coolant through the expansion tank(*). Otherwise, the heat soak can be bad enough to start warping things - namely the head - which tends to unseal the head gasket resulting in the dreaded blown head gasket scenario. Heat soak can also explain why you're driving around one day, everything seems fine, but maybe you have a too hot condition when you shut the car off and don't notice it (possibly combined with improperly torqued head bolts). When you go to start the car up the next day, things go very wrong from the start - hard starting, extra noises, white smoke out the back, car overheats quickly, etc. That would be a too severe case of heat soak that got you after the car was shut off.

(*)- One concept that I don't fully understand myself. -If you're overheating, isn't there pressure in the system forcing everything out? -So how does coolant get drawn into the system? You'd think the engine would have to be allowed to cool thus creating a vacuum to pull in the contents of the expansion tank. Gohim?, anyone?, how's that work?

[ This Message was edited by: Smoothie on 2002-06-24 01:54 ]

[larso]

When you over heat the expansion tank fills up and overfills. The only Time I've seen it get "sucked in" as you say is when the head gasket is blown. Coolant gets drawn into the cylinders and causes the coolant level in the tank to go down. That's the problem with 2.5 inch exhaust, once the cylinders fill up, the exhaust starts to fill up...then when you go to start the car up, you get nice blurps, pops, and green candy smell coming out of the pipe. You may even get a few fish and oysters coming out if you leave the car sitting long enough.

I've also seen the coolant get "sucked in" when a rad hose is cut or blown, since the coolant is going out and has to be pulled in.

If you do see the coolant getting sucked in, and there is no coolant coming out...I'd say the only possibility is that it's getting in the cylinders or in one of the oil passages in the head.