Engine cool down procedure

[vash]

so wouldnt any leftover heat just chimney out the big hole in the engine cover? i bet just popping the lid open would help alot. a fan blowing from the bottom up would speed things up.

[Wayne 962]

Originally posted by Evans, Marv
Remember, after you turn the key off, you're not adding anymore heat to the system. So it can only go down temperature wise, & you don't have a turbo to cool down.

No, that's not entirely true. You have a very hot engine that is in equilibrium with the cooling system when running. Then you shut off the cooling system and immediately remove all of the cooling air. The engine is still hot, but no longer being cooled. As a result, head temps tend to spike right after you turn it off.

-Wayne

[Grady Clay]

Wayne,

Welcome back.
We all know you have been moving Pelican. Now you get some rest and catch up on the posts.

Best,
Grady

[aigel]

Just shut it off and leave it alone. Once you turn that key, nothing moves. So what harm will the higher temps do?

If your car has hot start problems, something is WRONG. Carbs or not, it should start well when hot.

George

[Grady Clay]

George,

Some of us Pelicans don’t live in a clime where you can cut the air (fog) with a knife. Texas, Florida, or Colorado, high temperatures and heat soak on shut-down are serious issues. My mom (91) lives in N. Berkeley Hills and I’m out there regularly. I can attest the conditions are dramatically different from Colorado.

There was a thread a few weeks ago about A/C in an early 911 in very hot situations. The consensus was that all those problems were solvable with carefully extending Porsche’s great engineering.

Air cooling presents some unique thermal issues.

In the ‘70s several factory engineers and department heads visited me. We went for drives in 911s, 930s and 928s with my thermocouples attached. They had never seen such high temperatures outside Africa. This was their “American market” and they were concerned. I think most, if not all, of these issues have been addressed with the current 911s. Our challenge is to understand the issues, apply Porsche’s solutions to the older cars, and where none exist, find new ones.

Best,
Grady

[Wayne 962]

Originally posted by Grady Clay
Wayne,

Welcome back.
We all know you have been moving Pelican. Now you get some rest and catch up on the posts.

Best,
Grady

Still moving - the big move is this weekend...

-Wayne

[Wayne 962]

Originally posted by aigel
Just shut it off and leave it alone. Once you turn that key, nothing moves. So what harm will the higher temps do?

Yes, that's true. BUT, if you turn it off, wait 30 seconds, and then start it up again, then the engine temps have spiked, and you might do some damage. I recommend waiting at least 3 minutes or so before starting up a hot, air-cooled car again.

Originally posted by aigel
If your car has hot start problems, something is WRONG. Carbs or not, it should start well when hot.

Some cars have design defects that cause vapor lock (the 914 is one such beast). Everything can be working fine on that system, yet you may still have hot start problems.

-Wayne

[Mark sP]

When hot, my Audi always suffers from vapour lock. A real pig to restart sometimes after refuelling for example. Even with the extra little fan that blows air directly onto the fuel lines/injectors when I switch the engine off.

[bigchillcar]

Sounds a litte it over the top to me Daryl, probably can't hurt though.

on THIS board? over the top? what is that...?
ryan

[tkrefeld]

Do what the owners manual says.

[sundaypunch]

I'm with the "it can't hurt but why bother" crowd. The only real advantage I see is if you want to restart the car shortly after shutting it off. If you plan on doing that you probably won't bother setting up fans behind the car in the first place.

I also have a problem finding an electrical outlet at the mall.

[pmax]

Originally Posted by Wayne at Pelican Parts

No, that's not entirely true. You have a very hot engine that is in equilibrium with the cooling system when running. Then you shut off the cooling system and immediately remove all of the cooling air. The engine is still hot, but no longer being cooled. As a result, head temps tend to spike right after you turn it off.

-Wayne

Agreed.

Opening the lid after a spirited high revving drive during the cool down idle definitely helps the black beast.
The seals and gaskets say thanks and the metal doesn't groan as loudly
It's also the perfect time to check the oil, no loss after 500 miles, so far so good.

[ClickClickBoom]

Originally Posted by Joe Bob

Yup...turbo/blown only. Waste of time for an NA motor...

I idle my blown Dakota for two minutes before shutdown....

The cooling medium for all cars is air, some use oil to transfer heat to the outside of the engine and some use oil and water jacketing. The water jacketed engine still has cooling medium in contact with the hot areas, while the non-jacketed, oil cooled engine has lost circulation of the cooling medium after shutdown.