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View Full Version : Does it help or harm to leave the hood up after a drive?


mmmm7
04-19-2008, 06:12 AM
I know for a fact that coolant temp temporarily rises when you shut off the engine because there is no flow to carry the heat away.

Some bimmer owners I know leave their hood open for about 30 minutes before retiring for the night.

Does this help or harm in any way?

I know that some engines have aluminum heads and cast iron blocks. It might be an issue since aluminum cools faster than iron and might accelerate head gasket wear due to the two surfaces contracting at different rates.

Is this concern valid or am I just high?

e36m34life
04-19-2008, 07:52 AM
I think if the coolant system is properly maintained and there are no issues with the car, that its not necessary. But that being said, I also think if you park your car in the garage after a long drive, then it surely wont hurt to do so.

mmmm7
04-19-2008, 09:02 AM
I was actually thinking about putting a fan in front of the car with the hood closed so that it more or less mimics the engine-driven fan at idle. :dunno:

djfitter
04-19-2008, 10:32 AM
I know for a fact that coolant temp temporarily rises when you shut off the engine because there is no flow to carry the heat away.

Some bimmer owners I know leave their hood open for about 30 minutes before retiring for the night.

Does this help or harm in any way?

I know that some engines have aluminum heads and cast iron blocks. It might be an issue since aluminum cools faster than iron and might accelerate head gasket wear due to the two surfaces contracting at different rates.

Is this concern valid or am I just high?

Just an opinion here but here goes. Given that every time I drive the car, hard or otherwise, I don't have the opportunity to do it. I don't think doing it 1 time out of 6 or whatever, when parking for the night to be that beneficial. The motor stops creating any new heat when it shuts off. And one would think that the motor would cool down at a consistent rate with the aluminum and cast iron parts being in contact. If nothing else the aluminum may act as a heat sink and help dissipate heat. :dunno:
Now with that said, have I pulled into the garage and raised my hood? Yes. A couple of times when the temps were in the high 90's and I had just gotten home after a run down through Laguna Canyon to the 405 and then home. I live just a short mile off the freeway and I figured a little extra air to help cool the turbos couldn't hurt. :) And I too have thought about a fan. Like I said, it couldn't hurt.
My 2 cents.

dj

Jalli
04-19-2008, 10:41 AM
I was actually thinking about putting a fan in front of the car with the hood closed so that it more or less mimics the engine-driven fan at idle. :dunno:

If the car is really hot, doesn't the fan stay on even after you shut it off...? I seem to remember this happening several times to me..

djfitter
04-19-2008, 10:54 AM
If the car is really hot, doesn't the fan stay on even after you shut it off...? I seem to remember this happening several times to me..

Yeah I here noises from under the hood. I think the oil pump stays on for a bit if needed to cool the turbos. You're probably right with the fan too. :dunno:

dj

ProRail
04-21-2008, 01:07 PM
I know for a fact that coolant temp temporarily rises when you shut off the engine because there is no flow to carry the heat away.

Some bimmer owners I know leave their hood open for about 30 minutes before retiring for the night.

Does this help or harm in any way?

I know that some engines have aluminum heads and cast iron blocks. It might be an issue since aluminum cools faster than iron and might accelerate head gasket wear due to the two surfaces contracting at different rates.

Is this concern valid or am I just high?

When I had a Subaru with a turbo, the manual suggested that you let it idle for a few minutes after a hard drive so that the fluids would keep circulating. They didn't say anything about opening the hood.

Kzang
04-21-2008, 01:14 PM
I'm thinking if this actually benefits your car in anyway then it would be noted on the manual?

tturedraider
04-21-2008, 10:17 PM
Doesn't help, doesn't hurt.

mmmm7
04-23-2008, 06:17 AM
When I had a Subaru with a turbo, the manual suggested that you let it idle for a few minutes after a hard drive so that the fluids would keep circulating. They didn't say anything about opening the hood.

You should always let the engine cool off after a hard drive *but* I prefer not let it idle - instead, I drive easy for a few minutes (nothing over 2k rpm) which is normally the case when I'm looking for parking :D

Besides, driving slow and easy gets you more looks and double-takes ;)

Coconutpete
04-23-2008, 08:16 AM
When I had a Subaru with a turbo, the manual suggested that you let it idle for a few minutes after a hard drive so that the fluids would keep circulating. They didn't say anything about opening the hood.

That's because of the turbo though. You don't want hot a$$ oil sitting inside the turbo and cooking with the car shut off.

Same concept could apply to NA engines though, not sure.

Fudman
04-23-2008, 09:23 AM
If you have the V8, it's can't hurt. Those 540 cooling systems die a premature death (<80K) due to excess heat. Helping remove more heat can't hurt and can only help.

kevinp
04-23-2008, 11:07 AM
One thought would be to place a free standing fan just ahead of your radiator (like the kind used during dynamometer testing). The fan could be fitted with a thermostat and once the ambient temperature, adjacent to the car exceeded a specific setpoint, then the fan would cool down the car until it had reached the shut-off setpoint. The garage door would have to be open for this system to function properly. No need to open the hood, as the fan would force air over the car as if it were being driven on the road.

My free advice for the day:thumbup: