Engine cool down procedure

[fireant911]

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?

[Rot 911]

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.

[RickM]

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.

[Joe Bob]

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

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

[D@vid]

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

D@vid

[Bill Verburg]

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

[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.

[RickM]

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

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

[Grady Clay]

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

[tsuter]

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

[Crachian]

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.

[Grady Clay]

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

[Mark sP]

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.

[araine901]

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.

[svandamme]

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.

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...

[singpilot]

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.

[Emission]

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!

[addictionMS]

I always find a beer, helps with the cool down after a spirited drive.

Jim

[kqw]

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.

[B D]

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