Porsche Repair: 944 Running Hot, hairline cracks, smog test

Question
Hello Dave,
1988 944 Turbo, I have replaced everything, Thermostat (twice), hoses, water pump & auxiliary water pump, temperature sending unit, radiator, heater valve, intake gaskets, all belts, idlers and tensioners, balance shaft and a few other things, checked the fans too.  The car still runs hot.

Grant it I did not have it repaired due to over heating it just needed a 65,000 mile check up and I figured I might as well do everything.  But anyways it still runs hot.

Now I do live in Arizona and it was 109 out today but it still shouldn't run as hot as it does, even on the freeway with the air flow coming through it still does not cool off.  Any ideas or just blame it on Arizona.  It does run awsome in the winter!

Thanks in advance for your time.
Cameron

P.S. yes, the shop I took it to knows what they are doing and he is bewildered too.
Thanks again.


Answer
Hi Cameron.

Boy, when you say you replaced everything, you're not kidding!

From here, it doesn't seem like you missed much.  And with only 65,000 miles your baby should still be running fairly fresh.  It is hard to explain.  

Here are a few ideas...although they relate to engines with more mileage than yours.  They come to mind because I've had some overheating problems myself and have learned there are some concerns other than the obvious ones.

1.  If there is excess carbon in the combustion chamber the car will run hotter than designed.  A smog test (UGH!) should reveal this possibility.
2.  You didn't mention the radiator cap, although I'm sure you've replaced it many times.
3.  You also didn't mention the coolant reservoir.  The plastic can develop hairline cracks that cannot be easily seen, but that can allow pressure to escape.
4.  In a very weird case I found a buildup of corrosion that manifested itself as gel-like deposits.  You should have seen this if you replaced the water pump, as these tend to accumulate in the block.
5.  Lastly...is it remotely possible that the water temp may be registering high but is not really that high?  The gauges and senders are built to be accurate, but have you put another reliable temp gauge on and compared your readings?

OK...so I'm stretching reasonableness and I'm reaching for the obscure.  That's the best I can do.  If it's none of these, you'll have to move to Minnesota!.  Have fun with your little baby!

Dave