This was posted on the Maverick Region PCA Yahoo list by a long time Porsche tech.
J

.........It is truly amazing how much heat an air cooled engine can put up with. I'll give ya an example of the worst I've seen to date:
Had a person call and say they could not shut off their 993 engine. Turned
the key to off position and it just kept running. Owner was in a business
complex parking lot and due to be in an important meeting in just minutes.
Gave us a call and explained situation. Said tow company was at least 2
hours from arrival. The car was 45 minutes from us. I drove over there (took
me about an hour to get free) and arrived just as tow truck did. Car was
sitting there locked and running. All the instrument warning lights were
illuminated. Owner came out and gave me the keys. The temp gauge was pegged
and the engine was pinging like nothing I'd ever heard. Out of curiosity
before shutting off (figuring damage was already done) I gave it light
throttle application and it couldn't develop enough power to even raise the
revs off idle. It was too bad the owner didn't think to simply dump the
clutch and kill it (what I did immediately). When we got the call she
quickly explained the situation; announced she had to go right now and
"bye".
Turned out that the oil cooler fan relay had a bent tab inside of it and
the tab was feeding +30 (straight battery power) to +15 (key in run position
power) . This provided the DME system the power to stay powered up when key
was turned off ( a back feed if you will). Unfortunately there was no power
to close the fan relay because key was shut off and the oil cooler fan never
came on. After engine totally cooled and problem resolved we drained the oil
and took a sample (checked ok). Engine started and ran fine. No smoke, no
knocking noises, nothing. 2 years later this car is still driven daily and
you would never know this had happened to it. Any water cooled engine would
have seized up long before we got there. Air movement over top end helped
keep cylinders, heads, below melting point and enough heat was wicked out of
bottom end to save it. Obviously air cooling and synthetic oil was the key
to it's survival.
Cliff

 

Not sure I understand the reference to water cooled engine not being able to withstand sitting at idle for a long period of time. All my water cooled street cars are fine sitting at idle for extended periods of time in traffic. Did I misunderstand what you are saying?

 

Jay:
Great story.

Kary:
What he's saying is that a water cooled engine has one primary method to get rid of the heat of combustion; that is the liquid cooling system. An air cooled engine has the engine oil (12 qts in the 993) that acts as a "liquid" cooling system AND the movement of air over the cylinder heads and, to a lesser extent, the block itself. So an air cooled engine has the redundancy of a "backup" cooling system. Jay believes this kept the motor from frying in this case.

Reminds me of the WWII air cooled radial engines. They would fly home (land base or carrier) with cylinders and pistons hanging off the engines and the engine still running. Some of the photos are amazing. The Merlin and Allison liquid cooled engines were great, but not as forgiving to battle damage.

 

Ooohh, I see, thanks for the clarification.

 

& I can't take credit for the write up. I just drive them. It was written by one of our long-time, local techs.

 

:Cool: Ditto!