[ira968]

Had not driven the 968 for two weeks -- went straight to red on temperature guage. Was definetely overheated but coolant level was fine and no leaks. Guessing it is the thermostat stuck closed but know from my old Audi that things like disintegrating plastic water pump impellers can also be a cause. Can anyone provide a diagnostic procedure for this problem? A thermostat is $6, maybe I should start there?

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[sp4149]

[quote name='ira968' post='38966' date='Jul 27 2007, 05:25 PM']Had not driven the 968 for two weeks -- went straight to red on temperature guage. Was definetely overheated but coolant level was fine and no leaks. Guessing it is the thermostat stuck closed but know from my old Audi that things like disintegrating plastic water pump impellers can also be a cause. Can anyone provide a diagnostic procedure for this problem? A thermostat is $6, maybe I should start there?[/quote]

Changing the thermostat is not the easiest of tasks to start with. I'd check to make sure the fans are running wehn the temp goes up or the air conditioning is on. If they aren't running, fix that problem first.



-sp4149

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[SILVY968]

Right, Turn on the AC. It will force the fans on so you can check without overheating the car. If they do not go on check the relay. There is also a thermo sensor unit on the drivers side of the radiator, about 4 inches from the bottom( if I recall ) check the connector to it. and search this site for the way to check if the thermo sensor is working.



Check everything first before you jump into opening up the front of the engine.



Water pump/thermo change is not easy nor cheap!

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[Cloud9...68]

By chance had you flushed the coolant recently? I did mine a couple of months ago, but it's been a freakishly cool summer hear in central Texas (what Global Warming?...), so I didn't notice a problem until I very uncharacteristically drove it in some stop-and-go traffic on a ~90 degree day a couple of weeks ago, and noticed the temp gauge getting closer to the 10:00 oclock line than it had ever been before. So I rented ($0 cost) a cooling system pressurizer from Autozone, and found that there was still a ton of air left in the system, despite what I thought was a thorough bleeding that I'd done when I did the flush. After REALLY thoroughly bleeding the system, then taking it out for a long drive with the heater on full blast, bleeding again (found no air this last time), then topping up the coolant, it runs MUCH cooler now (barely gets above the 8:00 oclock line). So, before doing anything else, you might want to do a quick bleed of your system, since it's free. Good luck!

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[ira968]

It was a stuck thermostat. Probably original. My observations were if your cooling system is tight and you suddenly get a big jump (close to red line) in indicated temperature check your thermostat first by removing it, refilling and running the engine to see if the temp. returns to normal. Also, you can check your water pump by removing the bleed screw and running the engine cold -- if water squirts out the hole your pump is working. My sympton would rarely be electrical or sensors.

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[968rz]

Carefull on the "if water moves the pump is good: idea, when I got my car you could see the water moving but it would get hot (almost redline) when rolling down the road and letting up on the gas, turned out the vanes had come loose but would still turn (and pump) until there was high resistance from the coolant. Only found that by giving up and pulling the pump (t-stat made no difference.

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[DAK]

I just went through the pain of replacing a water pump at 90,000 miles on my '94 coupe. If you or your trusty mechanic goes to replace the t-stat, my advice is go ahead and spring for the water pump and new timing/balance belts while you're at it. Half the cost is just getting the front of the engine apart, makes sense to get some bang for your buck.

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[ira968]

I noticed several people in this post refering to the difficulty and cost of replacing the thermostat. It's really a fairly simple procedure and can be done in less than 30 minutes with simple tools. The only item you need to remove is the airbox and radiator hose at the water pump inlet -- just move the hose under the inlet and out of the way. Take a simple $.99 c-clip extractor tool (short punch like tool with a hooked end) and extract the clip holding the thermostat in the inlet. Replace it, put the c-clip back with the tool, refill the coolant and bleed the system.



If your mechanic is getting you for a waterpump, belts and major labor for a failed thermostat its time to find another shop.

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