strange coolant temp problem (cross post with 944 board)
 

Hey guys, need some help here. Searched here and at rennlist no luck. My 87 951 has a strange hot running problem. Start the car up and it can idle for ever and the temp never goes above the middle of the gauge (9 o'clock position) Start driving it and when it gets some load it rises to the top white mark on the gauge. Pull up to a stop and the temp starts comming down. Drive on the highway at 70 mph and the temp sits at the top white mark. Give it some load on the highway (like up hill with some boost) and it goes a little over the top white mark. Take and exit off the highway and come to a stop and temp comes down pretty quickly to the middle of the gauge.

This seems pretty strange, it cools down while idling at a light, heats up when on the highway.

I have replaced the pump and thermostat and bled the system many times and also had a shop look into it today. They bled it and said it was okay. Problem is they drove it around town stop and go so it never heated up much.

Clearly the fans work great because when the car is not moving it cools down!!

As a side note I have an intermittant heating problem. Sometimes there is heat in the car, sometimes not. When it is first started the heat seems to work, after driving for a while, it is intermittant. Today the shop said the control panel was malfunctioning and the two problems are not related.

I have bled the car hot and cold with pressure and without. The shop today bled it as well.

Where should I look next??

Cheers

Check to see if you have a hose (the lower one) collapsing and restricting coolant flow. Don't know what happens if thermostat is installed backwards.

What makes me suspect the hose is that the heater works when warming up but does not when hot. Hoses get softer when hot so the collapsing might only occur then. Just guessing...

I had a situation on my 951 a few years ago where it would get a little hot climbing mountains in top gear(about 2200 rpm) but was ok at idle and fine on the track in hot weather. In my situation, I replaced the water pump and the problem immediately went away. But you have already done that.

Thanks Lawrence, I will replace the lower hose as a matter of maintenance just to be sure. Not sure how to check it so replacement sounds the easiest. You are talking about the one from the pump to the lower radiator fitting in the passenger's side front of the car?

Cheers

Yes, that's the one. Hope it helps you out.

Thanks, I just took a look at it and it appears as though the line to the oil cooler is pushing down on it and constricting it a little bit. I will bend that line away from there when I change the hose.

Cheers

Just to update, turned out to be a plugged radiator. Had it flushed at the local rad shop and everything is good now!

Cheers

Glad to hear you figured it out.

Just to add to the knowledge base here. I had a slight overheating problem on my 951. Fans were running fine, coolant was new. Would run hot (though not overheat) at both idle and at speed.

When I removed my AC, the condensor (which sits in front of the radiator) was completely banged up. All of the fins were bent flat--blocking most airflow to the radiator. In my case, I removed the condensor and haven't looked back, but a new condensor would have solved the problem too.