Issues with cooling system?

I've done a lot of wrenching in my life. However, I've never worked on a cooling system till now. The car is a 1984 Porsche 944. Recently the temperature gradually was driving up onto the 3rd bar (meaning over half) which is approximately 97C. I figured it was the thermostat so i fully flushed the system and then replaced the thermostat with a 180F OEM thermostat. I then bled the system to the best of my abilities. It still had some air in it and would climb quite quickly to the 3rd bar. I bled it again after leaving it on stands for a few days and filling the coolant expansion with fresh coolant. Now it climbs VERY SLOWLY, but eventually at highway speed hits just /under/ the 3rd bar, so about 89C.

The issue seems to be that if i leave the car at a standstill and in traffic, the thermostat will open and it will cool down, the fans will kick in. So I know the thermo temp switch in the radiator is working, so are the fans. I can also turn on the ac and the fans kick in as well. If i turn the heater on full blast the temperature will go down slightly for a brief time. So the issue is not any type of therm switch.

The coolant does not bubble or boil. And I do not appear to be losing any coolant. I have verified and checked compression so I do not appear to be having a head gasket issue, and there is no oil on the dipstick either.

I replaced the cap on the expansion reservoir as it was not holding pressure and this did help. There is a significant difference in pressure. I am not seeing any visible leaks, but am unsure on how to do a leakdown test.

My other thought is that I may have a partially or mostly clogged radiator. However, these cars have an aluminum radiator with plastic bottom, so rust is pretty much unfathomable and unheard of, though corrosion may be possible.

Any ideas? I am going to attempt to replace with a lower temp thermostat and rebleed and test the radiator this weekend. Ideas are welcome. Please only serious answers, any bullcrap answers will be promptly reported to be removed. Thank you for your time for those serious enough to reply :)

2009-10-22T13:04:07Z

Allistair,

Thanks for your answer. I don't think the radiator has any air in it unless I was unable to get it out. However if it's clogged that's possible. Bleeding the system was a royal pain in the butt. The radiator does not appear to have been repaired, I also called a radiator shop and they said they are "obsolete" and do not make parts to rebuild them anymore. So the alternate is to get a new radiator if that is indeed the issue. Which it's starting to sound that way...

2009-10-22T13:15:02Z

Blackcat,

Thank you as well. I was kind of wondering if it's either a small leak somewhere or the radiator. I spoke with a rad shop and they told me i have the classic symptoms of a clogged radiator. Guess I'll test it this weekend.

2009-10-22T14:02:37Z

Theneelster,

It is N/A not Turbo. I can try flushing the radiator again this weekend. I will see if i can pull it out entirely and test it to make sure it's flowing okay. Perhaps pressurizing it and see if it's holding pressure (which it shouldn't be) or if it flows. Perhaps running some water through it.

The overflow hasn't kicked in yet, so it has not yet reached any kind of overheating temp. But i have a feeling if it continues that it will...

Anonymous2009-10-22T13:01:24Z

Favorite Answer

I'm thinkin the radiator is restricted in flow I,ve worked on alot of them and it may look fine from outside but inside its clogged.Some of the passages are so small that flushing won't clean them out.I just had to replace the radiator in my own ride,and it didn't leak a drop.

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Hank Scorpio2009-10-22T21:00:08Z

You need to flush the radiator then replace the coolant with a mix of 30/70 (as long as you live where it doesn't snow or go below freezing) and overkill would be adding something like water wetter. If that doesn't work, another possibility would be to add a second overfill tank to the system to spread the heat generated from your engine to more coolant.

I don't think the 944 is turbocharged but it might be; on turbocharged and supercharged cars, if you're running a lot of boost temperatures might exceed 180F and still be normal. I know the fans in my car kick in at 220F for heating problems and generally speaking I run 16pounds of boost through my supercharger and get around 180F on a hot day at my intake manifold.

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Anonymous2009-10-22T19:56:38Z

there is an internal leak that you arent aware of. plus, your not supposed to have "air" in your radiator. do it right this time. if not, buy another darn radiator.

edit: radiators are either all aluminum or plastic. unless its a piece of junk, that was cheaply fixed.

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