Overheating

[99C2_Riyanto]

Hi, I need advice on an overheating issue on my 3.4L 996 (built in Mar '98, engine replaced at 52K miles, currently has 105K miles total on the car).

First occurence of overheating was this summer on a race track. Since then, every time I do 5 hot laps, the water temp gauge goes all the way to the red zone. On stop and go city traffic, the needle moves higher than 190F, but still below the white line that is unnumbered on the gauge. On freeways, the car maintains 190F just fine.

I took it to an independent technician who recharged the coolant 3 times and replaced a fuse and 4 relays related to the fans. I was advised the fans would turn when powered with an external power source, but not when hooked up in the car. The technician ran out of ideas about the fans.

Then, I took it a porsche dealership. 1 hour of diagnostic later, I was told everything checked out fine. Nothing is found wrong with the car and the technician couldn't replicate the overheating. Well, duh, I've already told them the problem can only be replicated with certainty on the race track. The dealership then advised me to take the car to a radiator specialist for a power flush. This would cost $250 and I haven't done it since I can't see a good reasoning for it.

Any ideas? Do 996's fans turn on when the A/C is turned on as in most cars?

[Loren]

Fans should turn on (to high speed) when the AC is on.

Possibilities that come to mind:

- a partially broken water pump impeller

- a leaking head gasket (check your oil)

- temperature sensor, fan relays, should all be tested with a PST2 or PIWIS tester.

[Orient Express]

Have you ruled out that your radiators may be clogged with road debris? Do a search on "cleaning radiators".

The radiators on all 996,986,997,987s get clogged with stuff that gets sucked into the air intake and that will inhibit air flow. You need to take off the front bumper cover to clean the radiators properly. This can cause overheating.

[99C2_Riyanto]

Thanks for the replies, guys.

I'll look into your suggestions.

Loren, what's the easiest way to rule out the water pump impeller? The dealership noted the car has been checked with PST, but didn't say anything about PIWIS. Does PIWIS provide more information than PST? Dealership also noted the water temp was 205F after 50 miles of city driving and deemed it was normal. I personally don't think it's normal, since it was 55F outside and the car has always been able to maintain 190F since I owned it. This doesn't bother me as much as the fact that I can't go to any track event anymore since the car wouldn't go more than 5-7 laps before it gets into the red zone.

[Loren]

Yes, start with Orient Express's suggestion - I was assuming that your radiators were clear of debris.

For your MY car a PIWIS tester gives the same info as a PST2.

Other than taking the water pump off the only other way to look for a broken impeller is to remove a couple of the big hoses on the engine and check the coolant for small plastic pieces.

[Orient Express]

Here is an example of a typical radiator that has never been cleaned:

This car was experiencing significantly higher coolant temperatures until we cleaned out the radiators.

[99C2_Riyanto]

Thanks Orient Express. My mechanic told me he has done it. So, that one possible cause is checked off the list. I'll go to the track this Sunday to see whether that helps at all. It's impossible to make the car overheat with commute driving. Actually, yesterday, I revved the car to redline in 3rd gear to reach 99 mph and the temperature actually dropped, not rised.

Hopefully, this is my last question in this thread: Some people told me the car's fans are supposed to keep turning after I turn off the engine if it is at full operating temperature. I don't remember ever hearing the fans turning after I shut down the engine, no matter how hot it is. 996 carrera owners, do your cars do that? How hot does the water temp need to be to have that behavior going?

[Loren]

Thanks Orient Express. My mechanic told me he has done it. So, that one possible cause is checked off the list. I'll go to the track this Sunday to see whether that helps at all. It's impossible to make the car overheat with commute driving. Actually, yesterday, I revved the car to redline in 3rd gear to reach 99 mph and the temperature actually dropped, not rised.

Hopefully, this is my last question in this thread: Some people told me the car's fans are supposed to keep turning after I turn off the engine if it is at full operating temperature. I don't remember ever hearing the fans turning after I shut down the engine, no matter how hot it is. 996 carrera owners, do your cars do that? How hot does the water temp need to be to have that behavior going?

No, the radiator fans do not run after the engine is off. Same with the engine compartment purge fan.

If you are tracking the car it is always best to:

- take cool down laps if allowed

- come back to the pit area and let the car idle (fans will likely run) for at least 5 minutes.