Freakn' cooling system. - where to go from here
 

OK guys I'm not sure where to go from here. My 951 is having weird overheating issues.

My symptoms are as follows: while driving around the needle stays in between the two middle white marks but as soon as I come to a stop it starts to rise immediately and right when it gets near the upper white mark the high fan kicks on. However once the high fan kicks on the needle does not drop it just stays there and if I stay at a stop long enough the needle will begin to rise ever so slowly. Usually at this point if I rev the engine to 1200 RPM or more the temperature does begin to drop. It's as though there is not enough water flowing over the radiator at idle to allow the fans to cool down the coolant.

This leads me to believe either there is air in the system somewhere or that the water pump is not circulating enough coolant at idle.

I have installed a new water pump and I've bled the system about 20 times. Everything from squeezing the lower hose and cracking the nut to renting a pressure pump and pressurizing the system to bleed it. I've done that about three times. Each time when I crack the nut at the upper hose coolant comes out immediately, there is no air that escapes. When I installed the water pump I marked the pulley shaft to see if there would be any rotation relative to the pump pulley and there is not. Also I check to see if the impeller was binding on the block and there isn't.

Is the low speed fan working at all?
I'd suspect fan switch or fan relay. Fan switch has a low and high speed setting, maybe your low speed side is fried.

Both fans are working properly

Is the timing belt tension tight enough? If it isn't the belt might slip on the pump. Second, is it possible there's a lot of debris in the A/C and engine radiator?

I'm pretty sure the belt is tight enough. The last time I tensioned it with the arnworx tool I couldn't barely rotate the pulley with my hands once all the tensioning was done. AC radiator is pretty clean and the radiator is new as well.

Thermostat? When mine went bad at a stop it would rise to the top white mark and high speed fans were on it didn't move. When I started reving or rolling it did better. I changed the thermostat and it all went away. Probably not it but worth a shot if you haven't changed it.

Thermostat is new too. I'm pretty sure it's working because the temp drops when it first opens up. After that all is fine as long as I'm moving. It's when I come to a stop after I'm fully warmed up I end up having issues. Mind you it takes about 5 min of sitting still before the high fan kicks on.

You said both fans work but do they only work on high speed, or both work on low?

Both fans work at their proper times. But even if both fans only worked when the high fan kicked on shouldn't I see the temp drop when they did?

It seems there are three basic possibilities ( but if you know another please let me know):

1. Air is still somehow trapped in the system
2. My water pump is faulty somehow
3. My thermostat is not completely opening

I've tried remedying item number 1 so many times I've lost count so let's say it's not that for the moment. If item number 2 is correct I'm not sure how I could determine that, so for the moment but put that one aside as well. That leaves item number 3. I think I will try replacing the thermostat to see if that cures the problem. I really hate to have to drain and bleed the system again but of all the options it seems it's the one to try at this point.

I'll probably try to drain it next weekend so if any of you Porschephiles can suggest something else in between time please don't hesitate to let me know thank you!

UPDATE

I just pulled the thermostat. The one thing I did note is that I was able to turn the thermostat while the clip ring was still in quite easily. The thermostat has the thin seal around the edge as I recall there was also a thicker one - should I have used that one?

The thermostat should fit tight when installed. You probably need the thicker gasket. Are you using the correct Wahler thermostat? Some other brands have a smaller opening which can limit flow. Are all the bumper air ducts in place & the rubber seals between the radiator & the a/c condenser? Are the fans pulling air in from the front? I seem to recall someone saying the fans could be installed in reverse, but I could be wrong.

If the t-stat has any play in it, fore and aft, you will need to get a spacer for it and place it under the snap ring. I think that pelican has them...This will make sure that it is seated hard against the inner portion of the pump. The little wiggler (if you have one) needs to be up..so that it is higher than any other part of the T-stat. This is done so any trapped air can be bled out...Hope that this helps some..

I see ducts to the left and right of the center openings in the bumper that look like the would cool the brakes but the only other duct I see is the one that routes the air to the IC. As for the seal I'm not sure how to tell if it's installed correctly. I remember a foam strip that came with the radiator but I don't recall how I installed it. I wasn't sure what it was for.

Maybe try a new rad cap.

Did that to no avail.