Engine cool down procedure
 

As the warmer weather is arriving here in the south and the ambient temperature is beginning to increase I have developed a ritual immediately after putting my car away and I am curious if anyone else does anything similiar:

After taking my car out for a spirited drive I park it in the garage, open the engine lid, and place a box fan near the rear of my car to remove the excess and stagnant engine heat. My primary mission is to keep the hot exhaust temperatures from radiating to the oil lines and other engine components thus raising the temperature above what I had experienced on the road. I normally run with the fan on medium just so that it will provide some air movement (without getting into a thermal shock situation) and thus prevent further absorbtion of the heat that would occur in the first few minutes after shutting down the engine.

My goal is to add to the longevity engine/engine oil. I know these cars run perfectly fine when allowed to cool down naturally but is there any gains by using this slightly forced convection of air?
:confused: :confused:

Doesn't hurt anything, but I doubt that it is going to markedly increase the life of the engine. Maybe the engineer guys will jump in here, but I don't think there is much of a temperature spike in 911 engines when you shut them down.

The only cool down time I'd ever do is after a spirited drive in a turbo.
Up to five minutes at idle to circulate the oil, cool things off and prevent coke build-up.

There also used to be a pre-start and post-shut-off, pressurized oiler to automatically do this. Don't know if they are sold any longer.

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

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

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

D@vid

Sounds a bit much to me a well, I always let my turbo spool down for a minute or so, and a cool down lap(2 would be better) is always a good idea

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.

Here's a Pre-Oiler http://www.pre-luber.com/preluberproducts.htm

And After-Oiler http://www.accusump.com/acc_products/acc_turboiler.htm

You are correct, the issue is there are parts that are normally cool while running yet heat soak to high temperatures after shut-down.

Do just like a cool-off lap at the track where you buzz around at lower speed (lower HP demands) and high revs. The high revs keep the cooling air flowing and the oil circulating to the coolers. Another idea is to turn off the A/C just prior to getting home. The fan is an excellent idea and many use it at the track.

Fuel injected cars can boil the gas at the injector, causing hard start-up. This is particularly true with CIS and even MFI.

The issue of heat soak is extreme with carbureted cars. The intake manifold and carb operate at below ambient temperature while driving. This is due to the latent heat of vaporization of the fuel and the air pressure drop from ambient. After shut-down the high heat from the head transfers up thru the manifold to the carb. This causes the fuel in the float chamber to boil and fill the air filter assembly with just gas vapors. The combination of no fuel in the carb and no air in the intake makes for difficult starting. In extreme cases the carb can boil dry and the temperature get outrageously high to the point where the brass float will expand and stick down in the open condition. Disaster follows.

I think all carbureted 911s should use two or three of the phenolic spacers Porsche supplied on ‘71Ts. They can be sized for any intake.

A track trick I use is we have a pair of aluminum baffles outboard alongside the carbs. After coming off the track we dump about 5# of ice in them to keep the manifolds and thereby the carbs cool. The ice melts by the next session and the engine fires on the first ¼ turn with none of the characteristic (C6 cams, 46IDA, race plugs) poor running on start-up.

Just the opposite is true in extremely cold weather. You want to put the 911 away hot to dispel as much condensation as possible.

You need a house where you drive long up-hill to it in the winter and coast long down-hill to it in the summer.

Best,
Grady

Such worry worts! I can't believe my cars still running all these years! And its got a turbo! :)
Track time excluded!

Like Alabama, it gets pretty hot here in Texas. On those really hot days, I would pop open the engine lid after parking in my garage. The blast of hot air that was "released" was, well, really hot. And I can't help but think that helps at least a little. I think it may be hard for some people living in more moderate climates to understand how hot it really gets down here - temps near the road surface of 150F+. Every summer kids die in parked cars.

BTW, didn't somebody take post-shutdown cylinder head temperature readings last summer? I'm too lazy to do the search.

Guys, this not over the top in hot weather.

THE limiting factor with air cooled 911s is temperature. This is why we can’t use as high CR as water cooled 911s. It limits the ultimate power compared to water cooling. Porsche went to water cooling because it is cool, pun intended.

The water cooled 911s are at lower temperatures while operating and the water cooled components don’t rise in temperature after shut-down. The coolant may boil in certain locations but that is a cooling effect. Yes, the cool fuel components will see a rise in temperature after shut-down, just not as much as the air cooled types. Both benefit from a fan cooling the engine after shut-down.

Years ago, I recommended to Porsche a one-way clutch at the fan pulley so the alternator could be electronically driven as a motor and keep the fan operating for a period after shut-down.

I don’t think thermal shock is an issue in this situation. You can take a hot 911 and run a garden hose in the fan while revving at 4000 (not recommended) without any obvious detrimental effects. I have done that many times, however I admit I only spritz a little until the engine has cooled somewhat.

A major part of the temperature issue is the spike in temperature just after shut-down. That is particularly worrisome with components that normally don’t see high temperature during normal running. There are fuel components that normally function in the -40F to +140F range yet must withstand shut-down temperature spikes of 400F. All the stuff in a 911 engine can survive it just fine. My feeling is “Why press your luck.” when there are alternatives.

Daryl, I like your fan solution. To directly answer your question, yes there are benefits to be gained.
Besides, it keeps your garage cooler. The only down-side is you have to remember not to back over it in the morning.

Best,
Grady

I always let the quattro sit at idle for 3-5 minutes to let the turbo cool off. I also try to make sure that last 2 or three miles prior to arriving home are driven gently.

With the Carrera I just switch her off.

Grady is spot on the carb motors. Mine runs like ass if I try to start after it has been warmed up. No matter how long I let the fuel pump run prior to starting or how long I let it run at idle. Until I get it moving an flush out the air it just pops and snarls and get down right grumpy.

If I drive mine in hot weather (105-117) I let it run for about 1 Min with the deck open then I turn it off and turn the AC in my garage (Yep A/C is a must in the garage of any tinkerer in AZ) on to let it cool down. If I dont use the AC in the garage the temp will riase 10 degrees inside and if its over 100 it get down right unbarable.

that's incorrect , if you just drove hard
and you shut down.. your temperature WILL go up at first

so it doesn't hurt to ease up on your engine in the last 5 minutes before your shut down, but unless your are running really really hot , untill the last second before parking your car in the garage.... the car will not need extra cooling...

I will quite often see 210 on the oil temps as I am turning into my canyon on the way home. Ambients on the desert floor at the freeway offramp will be 120F. I then climb almost 1800 feet elevation in 11 miles, then up a desert canyon road at reduced speeds. I will typically turn the air off at the bottom of the hill. The heat that streams from the engine once off seems no hotter than when parked down in town. The oil temps are down 50 degrees if I start it up again 30 minutes later.

I guess the fan couldn't hurt, but other than thurning the air conditioning off, I have never felt the need to baby mine. I have the Carrera cooler, but no fan.

There is something else that is not being addressed - the extended life of electronics, hoses, and belts from the reduced heat in the engine compartment.

After shutdown, underhood temps spike as there is no more fan movement of air. Those very high temps rising off the exhaust and block (300F+) cook the electronics, hoses, and belts. I open my decklid to prevent this cooking, not to add longevity to the oil.

I like the electric fan in the garage idea - I need to go get one!

I always find a beer, helps with the cool down after a spirited drive.http://www.pelicanparts.com/support/...s/beerchug.gif

Jim

When I lived in AZ. and after a spirited run in 100+ degree temps, I would pull the car into the open garage and let it idle for a few minutes. I have a thermo-switched fan on the front cooler and when the fan turns off, I shut the car down.

I switch a small computer fan on that shoots on my cool collar the last mile home. ;)

heat rises right?
 

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.

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

Wayne,

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

Best,
Grady

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

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

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

-Wayne

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.

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

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.

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

Do what the owners manual says.

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.

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.

http://forums.pelicanparts.com/uploa...1405957236.jpg

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.