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leave the engine lid open

 
Old 09-13-2018, 09:10 PM
  #1  
marucus1
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Default leave the engine lid open

has anyone done it
open the lid after a drive (20-30 minutes or more) casual not sprint
reason: to let the heat out and prolong the (plastic) component in the compartment
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Old 09-13-2018, 09:14 PM
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platinum997
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Subscribed .. have heard many mixed opinons on this. My understanding is the fan on the decklid is sufficiant and actually does a better job than leaving the lid open.
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Old 09-13-2018, 09:17 PM
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mikemessi
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I do it after every drive when parked in garage. Lock doors and the light goes out after a couple minutes. There will be no data for or against this just opinion.
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Old 09-13-2018, 09:22 PM
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Used to be quite common to do on the old air-cooled cars... It kind of makes sense, letting the hot air out to cool the engine faster. I've done it on track days.
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Old 09-13-2018, 09:51 PM
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I do it after every track session and when I return home for longer runs.
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Old 09-13-2018, 09:52 PM
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Tcc1999
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I don't think it is opinion (not to leave the engine lid open) but a matter of physics. If you open the lid the fan will not engage and your engine is radiatively cooling. There is nothing wrong with this, but if you leave the lid closed and allow the fan to work it will move air through the engine bay until whatever temperature Porsche figures is okay and then it will shut off. The point is that you are rushing cooler air through the engine bay, this air gains heat (while the engine looses heat), is pushed through and replaced with new air that further cools the engine. There is nothing wrong with opening the lid to cool the engine, it just isn't as efficient (unless you have a fan or two set up blowing ambient air through the engine). Either method is probably fine under many circumstances so whatever makes you comfortable is fine. The thing to remember though is that your car is not a 2,000 year-old piece of china, it is built to take the type of heat build-up that comes with spirited driving. I wouldn't swear to it, but I'd guess that PAG engineers do consider this when they program the fan to come on when you stop driving.
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Old 09-14-2018, 08:55 AM
  #7  
Petza914
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Originally Posted by Tcc1999 View Post
I don't think it is opinion (not to leave the engine lid open) but a matter of physics. If you open the lid the fan will not engage and your engine is radiatively cooling. There is nothing wrong with this, but if you leave the lid closed and allow the fan to work it will move air through the engine bay until whatever temperature Porsche figures is okay and then it will shut off. The point is that you are rushing cooler air through the engine bay, this air gains heat (while the engine looses heat), is pushed through and replaced with new air that further cools the engine. There is nothing wrong with opening the lid to cool the engine, it just isn't as efficient (unless you have a fan or two set up blowing ambient air through the engine). Either method is probably fine under many circumstances so whatever makes you comfortable is fine. The thing to remember though is that your car is not a 2,000 year-old piece of china, it is built to take the type of heat build-up that comes with spirited driving. I wouldn't swear to it, but I'd guess that PAG engineers do consider this when they program the fan to come on when you stop driving.
+1

The engine is also designed to cool by moving air from the top through to the bottom, which is why the fan spins the direction it does. Radiatively cooling it has the heat moving in the other direction. Leave the lid closed and let the fan work to cool it properly.
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Old 09-14-2018, 10:37 AM
  #8  
yvesvidal
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I always open the lid in my garage after using the car. Most of the heat that causes damages is immediately extracted and that protects all the plastic parts.

The way the fan is designed on a Carrera is non-sense. Heat always rises. Cool air is located near the road or surface, especially in a garage not submitted to solar direct exposition.
It should extract air from the underneath of the car and move it out of the lid, instead of fighting natural and physics laws.

As a proof of my discipline of opening the lid, I can tell that the coolant tank is impeccable and does not have a trace of cracking. For a 12 years old car, prone to this kind of issue, it is not too bad.

Yves
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Old 09-14-2018, 11:34 AM
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Johnny DB
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I always open it. Heat rises and I'm also not subjecting the plastic and rubber to unnecessary heat in an "oven". Even right after the fans kick on, open your deck lid and see how much heat is in there! I let the fans do their job when I go to the grocery store or wherever but at home, lid is always open.
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Old 09-14-2018, 11:37 AM
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Tcc1999
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Originally Posted by yvesvidal View Post
I always open the lid in my garage after using the car. Most of the heat that causes damages is immediately extracted and that protects all the plastic parts.

The way the fan is designed on a Carrera is non-sense. Heat always rises. Cool air is located near the road or surface, especially in a garage not submitted to solar direct exposition.
It should extract air from the underneath of the car and move it out of the lid, instead of fighting natural and physics laws.

As a proof of my discipline of opening the lid, I can tell that the coolant tank is impeccable and does not have a trace of cracking. For a 12 years old car, prone to this kind of issue, it is not too bad.

Yves
If this practice works for you then , but I think you have the physics slightly wrong. Of course hot air does rise, but when you open the lid to cool your engine the heat exchange with cooler air immediately cools the exposed surfaces of the engine. The heat sink below these surfaces will lose heat by conduction to the upper surfaces (which gain heat energy) and, in turn, the upper surfaces will cool by exposure to the cooler air. Eventually the system will equilibrate. This is effective but not optimal. In contrast, if you leave the lid closed it acts as an insulator and hot air is not allowed to escape by the fan taking in cooler air from above and passing it through the engine frommtop to bottom. This may seem counter-intuitive but if you think about it it makes sense. The nature of hot air is to rise so the fan is introducing cooler air at the heat boundary, there is a heat exchange, and the air is directed down and out. Over time the cooler exterior air reaches further into the engine bay and cools parts of the engine that would otherwise radiatively cool at a much slower rate. That is the best I can do without equations and $0.75 cent words. If your system works for you and you are satisfied though, cast physics aside. it is a testament to how resilient the PAG engine is. (If you want to test this, bake something in the oven, when done, poke a few holes in it, wrap it in foil leaving the top and bottom exposed and put it on a wire rack, then, over time, measure the heat at the center. Now do the same thing except place a fan on top pushing air downward. I’m pretty sure that you will find that rate of cooling for the latter method much more rapid.). Anyway, if you’re in NC stay safe weathering the storm.
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Old 09-14-2018, 11:55 AM
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This is for the 996TT but gives you an idea of temps and start/stop cycles:
"Two-speed compartment scavenging blower

To prevent components from heating up excessively especially as a result of radiated heat from the exhaust system, the fuel pump relay immediately activates the engine compartment scavenging blower (stage 1) if the engine is running at idling speed or if the ignition is switched on ( for longerthan 1 sec.). Stage 2 is actuated by the engine compartment temperature sensor.

Caution! Safety note:Special care must be taken when working on components in the engine compartment with the engine running or with the ignition switch on.

Switching stages:

1st stage:
Ignition ON (for longer than 1sec.) or engine running (actuated by fuel pump relay via booster resistance cable).

2nd stage:
At coolant temperature of approx. 105 °C or engine compartment temperature of approx. 78 °C (OFF at approx. 60 °C).

After-run phase:
Requirement: Engine compartment temperature with ignition OFF > 25 °C

After-run ON:
For 3 minutes at engine compartment temperature > 78 °C. The switch-on condition of > 78 °C is then checked every 10 seconds.The after-run phase is active for max. 40 minutes."
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Old 09-14-2018, 11:58 AM
  #12  
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Originally Posted by yvesvidal View Post
I always open the lid in my garage after using the car. Most of the heat that causes damages is immediately extracted and that protects all the plastic parts.

The way the fan is designed on a Carrera is non-sense. Heat always rises. Cool air is located near the road or surface, especially in a garage not submitted to solar direct exposition.
It should extract air from the underneath of the car and move it out of the lid, instead of fighting natural and physics laws.

As a proof of my discipline of opening the lid, I can tell that the coolant tank is impeccable and does not have a trace of cracking. For a 12 years old car, prone to this kind of issue, it is not too bad.

Yves
True, heat rises but the heat that's rising is coming from the hottest part of the engine - the headers and it's rising and flowing over the "delicate" engine parts above. I'm inclined to let the engine compartment fan blow the hot air out underneath the car. I sometimes supplement that with an external fan blowing that heat out of the garage. But having said that, I've vented the engine by opening the lid also. Your car so your choice - both methods seem to work in the hot climate of Texas.
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Old 09-14-2018, 12:21 PM
  #13  
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Does someone have a handheld infrared temperature gun that can test both methods? Maybe 5 min after shutting down, and then 15 min after shutting down. If the test is done properly it would be interesting to see the results.
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Old 09-14-2018, 12:30 PM
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996AE
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Im old school and always open lid after pulling into garage. I placed a large fan on the work bench that blows cool air down onto engine bay, lid up. As a nut P car owner since 16 years of age I have always done this.

As a race car driver we always lifted the hoods and many times placed fans on engine at track. I know its old school but heck I am old and habits die hard I guess.
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Old 09-14-2018, 01:02 PM
  #15  
saabin
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On the turbo (not sure about the N/A cars), the engine compartment temp sensor is just behind the Y pipe on the right side.. I wonder if Torque (or Durametric) can log this sensor value? I have seen intake temp and coolant temp PIDs before, but I dont know about the compartment temp..

Anyway, if it's there it would be easy to do an experiment to see which way cools faster, etc. The proof would be in the data I'll check this weekend with Torque to see if it has the PID in it's list..
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