Engine compartment fan
08-14-2015, 09:36 PM
#1
Racer
Thread Starter
Engine compartment fan
Today I tried to get the engine pretty warm (oil got up to 225 on gauge) to check the engine compartment fan. When I shut off engine, while key is still on, the fan runs (as do the radiator fans too). However when I turn key off, the fan shuts off. Is this right? I would think the fan would run while off, and I take key and walk away. The book says it monitors engine compartment temp for 30 minutes and may come on. But if it is running with power on, it must be hot enough in there for the fan to come on even with power off and key removed. I don't want to cook my engine...
08-14-2015, 10:35 PM
#2
That seems normal-
on my 07 997.1TT eng fan will come on sometimes 10-15 minutes after car is shut off & run for few minutes- sometimes back on again- It never comes on immediately after turning car off- usually awhile afterward- hard to figure out it will come on though-after hard run fan won't come on all the time, but sometimes after limited use at lower rpms, when i go into garage the fan is on 10 or 20 minutes later.
i try to cool down car on last few miles home by keeping revs down & also let my car idle in garage for few minutes before shutting off-
on my 07 997.1TT eng fan will come on sometimes 10-15 minutes after car is shut off & run for few minutes- sometimes back on again- It never comes on immediately after turning car off- usually awhile afterward- hard to figure out it will come on though-after hard run fan won't come on all the time, but sometimes after limited use at lower rpms, when i go into garage the fan is on 10 or 20 minutes later.
i try to cool down car on last few miles home by keeping revs down & also let my car idle in garage for few minutes before shutting off-
08-15-2015, 07:55 AM
#3
Trucker
Rennlist Member
Rennlist Member
This is normal. As the heat rises with car parked the fans cycle. The 996GT2 fans are the worst in cycling...
When I get home I always park, lock, and open the engine compartment lid to let heat escape via convection. That way the fans do not come on either.
When I get home I always park, lock, and open the engine compartment lid to let heat escape via convection. That way the fans do not come on either.
08-15-2015, 08:07 AM
#4
Three Wheelin'
I dug into this and after lengthy post reading decided to leave the lid closed after a hot lap. Seems the fan is designed to push cool air down thru the engine bay and finally out past the hot exhaust and turbos. Opening the lid allows the hottest parts below to cook everything above with natural convection. Else Porsche would have reversed the fan.
08-15-2015, 11:58 AM
#5
Racer
Thread Starter
ok, so it sounds like there are multiple stages on this fan. My 993 does that, all kinds of servos clicking and fans going on/off as the car sits there in the garage cooling off... An eletrical nightmare...
08-15-2015, 12:52 PM
#6
Trucker
Rennlist Member
Rennlist Member
I dug into this and after lengthy post reading decided to leave the lid closed after a hot lap. Seems the fan is designed to push cool air down thru the engine bay and finally out past the hot exhaust and turbos. Opening the lid allows the hottest parts below to cook everything above with natural convection. Else Porsche would have reversed the fan.
I do the opposite route since I don't want the key off current draw,and years ago when I was "serious" and tracked cars, I had my car(s) thermocoupled for (various) heat management, and lid open no fan and temps drop very quick.
The fan direction on these cars has to do with a lot of things such as: 1) top of the trunk lid (zone) is a low pressure (aero) point and at speed you would not want to blow air up and cause turbulence and ruin the aero. (this is why your spoiler raises up to get into the higher pressure zone for aero down lift). 2. Fresh air intake sits back there, and you would not want to suck hot air back in at stop and go. As tar as rise over ambient (ROA) after key off the best answer and least convenient way is to open lid and blow external fan at engine. That's all from me...too much typing for one day!
08-15-2015, 01:15 PM
#7
Race Director
Today I tried to get the engine pretty warm (oil got up to 225 on gauge) to check the engine compartment fan. When I shut off engine, while key is still on, the fan runs (as do the radiator fans too). However when I turn key off, the fan shuts off. Is this right? I would think the fan would run while off, and I take key and walk away. The book says it monitors engine compartment temp for 30 minutes and may come on. But if it is running with power on, it must be hot enough in there for the fan to come on even with power off and key removed. I don't want to cook my engine...
Even though the fan is running when I shut off the engine once off the fan stays off for a while. This makes sense as the constantly running fan helps keep down engine bay heat so is it unlikely to be hot enough to trigger the fan to come on immediately after engine off.
I might also add that I let the engine idle some before shutting it off -- this is per the factory manual -- so the engine bay temperature is below the temperature the engine compartment fan is triggered.
But occasionally when using the car for my DD needs I return to the car shortly after parking the car I hear the fan running.
I'd say the behavior you are experiencing is normal.
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08-16-2015, 04:03 PM
#8
Racer
Thread Starter
You guys were right. I came home today after a hot run, let it cool off a bit at idle (fan running), shut off engine (fan off), went inside, made a sandwich. Back on front porch eating my sandwich, maybe 15 minutes later, fan comes on. All is right in the world... 
