Legoland951

I have a 85.5 944 n/a that overheats only during idle. The water in the coolant tank is not hot but the water in the engine is boiling over. When I rev the engine to about 1500 rpm with the car stilling still, hot water circulates through the radiator and it stops overheating. I even took the thermostat out and still does the same thing. Both fans turn on when the engine rpm is higher and circulating thru the radiator. It just doesn't seem to circulate water during idle. I looked at the waterpump pulley and it turns well during idle. What could it be? I changed the radiator and it does not have a blown head gasket because its not losing coolant unless it overheats. There is no mixing of water and oil. Anyone encounter something like this before?

MHT

I have seen a similar problem, in my case it turned out to be the water pump itself. The pulley looked fine from the outside but once the pump was removed you could see that the impeller was spinning on the shaft. If your radiator is cold and the hoses are hot, you have taken out the thermostat and there is still no circulation, then I would suggest removing the pump.

Good luck Mark T.

ahofam123

I would think that either the water pump is going or the radiator could be clogged. Since you replaced the radiator though, my guesses are on the waterpump.

PeteL

Double check belt tension. The w pump is driven off the back of the timing belt. If it is loose, then the pump might not be moving or is slipping at idle.

Tabor

You could be low on coolant. I had the exact same symptoms and I was just low on coolant (I have a slow leak).

Mike S

Have you pressure tested your system also? I had a similar problem where I was overheating all randomely. The shop pressure tested it, turned out fine. The solution: Bad ground in the temp gauge. Ugh!!! Stupid grounds.

Chris 968

I had similar problems with my 968 when the heater control valve was going out. It was allowing air to get into the system, causing it to overheat when at idle.

I don't know if a 944 would have the same issues.

billybones

Get unerneath the car and check the fins on your AC and radiator and make sure they are not all bent up and clear all the way thru. with debris. I use an old stiff tooth brush to clean them out and straighten them. It does not take to much to kill the air flow ability to cause overheat situations. just one old maple leaf will impeede air flow or heat release. HTH

Legoland951

I bled the system and it ONLY overheats during idle. When I rev the engine even when the car is stopped, it circulates. Also, The fans are working properly so its not ground or sensor related. Even the thermostatic fan switch is new and the lower temp one. I am running out of options. I look at the pulley at the pump and it turns with no problems during idle so its not the belt tension. Its really annoying. I am not sure how air can get into a pressurized system. I would imagine it goes the other way as water is boiled inside the system.