up4speed

I have a 2001 TT, I'm still new to the car and trying to figure out what is normal, and what isn't.
After reading hundreds of posts regarding the engine compartment fan, I still don't know if mine is behaving normally. It's possible that mine may be different because my car is not 100% stock anymore, and I think that may causing confusion for me.
I was under the impression that the fan should be off until the engine bay reaches a certain temperature while the engine is running (I think it was 170 deg.), and when the engine and key are off, it turns on if the engine compartment gets up to about 140 degrees or something like that.
The way mine is operating:
Cold engine Key on, engine off - fan is off (that's good)
Hot engine, engine off - fan kicks on when heat builds up (that's good)
BUT.......
Cold engine, fan starts immediately when engine is started and runs the whole time that the engine is running. That's the confusing part because I thought it supposed to kick on only when the engine bay reaches a certain temperature and cycle off and on as needed to keep the engine bay temps down below that 170 degree mark.

If my car is not behaving normally, I may have the answers, but would like confirmation from someone who knows for sure.
There are 2 possibilities for the fans behavior.

1) My spoiler was stuck in the down position so I installed the fixed spoiler kit from e-bay. The instructions said to install the fixed spoiler harness in order to prevent the error light from coming on. I installed the harness # 996-612-070-04. Possibly this harness was designed for the GT cars and some how keeps the fan on?

2) The car has an ECU tune from Ultimate Motorwerks (UMW), possibly intentionally programmed to keep the fan on?

Any ideas?

up4speed

Update:
Kevin from Ultimate Motorwerks responded back to me already! Apparently, the fan control has nothing to do with the ECU tune and relies on the engine compartment sensor to kick the fan on.
So the issue is either with the fixed spoiler harness, or something completely different. Or it's normal for a 2001 996 turbo

Macster

My info is the engine compartment fan has two modes of operation.

These are controlled/selected by a fuse.

If the fuse is absent the fan only comes on when the engine compartment temperature reaches some temperature threshold. I do not recall the temperature threshold.

After the engine is shut off the fan can come on if the engine compartment temperature reaches some temperature threshold.

If the fuse is installed the fan comes on at engine start and remains on regardless of engine compartment temperature.

After the engine is off the fan can still come on if the engine compartment temperature reaches some threshold.

Why these two modes?

What I recall (from some TSB IIRC) is in some areas having the fuse installed is preferred. The reason is that there is a risk of a twig falling on the engine compartment lid and jamming the fan. If the fan is fused to come on from the get go its starting torque is higher. The idea (hope?) is this will be sufficient to snap the twig and allow the fan to operate.

The starting torque of the fan motor is for some reason less if the fan is fused to only come on when the engine compartment temperature gets too high.

My 03 Turbo's engine compartment fan runs all the time.

Oh, IIRC the fuse is C5 and is a 5A fuse. The other fan fuse is B4 and is a 15A fuse.

up4speed

Thank you!!!
I've been going crazy trying to find something that is consistent, there are many different opinions. I also posted on other Porsche forums and got varied responses.
I did however get others to say that it's normal for the fan to always be spinning on a 996TT.
Thanks for explaining and being thorough with the fuse set up. It makes sense (other than the twig theory). I would think that the climate would determine whether the fuse is installed or not. I just pictured a car that was used all year round (mine isn't), parked in a snow storm. What would happen when there is snow/ice packed in the fan and the car is started? If the fuse is pulled, the snow would melt before the fan kicks on, so there wouldn't be an issue with a stuck fan. My made up theory sounds better to me than the TSB explanation with the twigs....What area of the country has a higher percentage of twigs? LOL
Anyway, thanks again. I really appreciate it, and I'm happy that there is no concern with my car.

993GT

IIRC, the engine-bay temp. threshold is 90C

Macster

My additional comments regarding the twigs was not a theory. Unfortunately I can't put my hands on the document from which I read this.

I agree it sounds, reads, a bit goofy and I don't know about snow build up.

It may have something to do with if the fan motor is fused to come on at engine start time and if the fan is jammed this would trigger a warning light and allow the driver to clear the obstruction.

This would also have the driver turning off the engine and thus the fan motor fuse would be saved.

OTOH, if the fan motor was fused to only come on when the engine compartment temperature reached some threshold and then the warning light came on the engine compartment temperature would already be quite hot. The fan motor fuse would likely blow as well so even after the jam was cleared the fan motor would not operate.

Then there is the situation where the fan is jammed but the driver doesn't know because the fan motor is not triggered to come on while the car is being driven. The driver parks the car and then the fan motor is triggered to come on but of course the driver has no clue there's a problem.

The fuse would likely blow and there is no engine compartment cooling taking place at this time. The next time the driver got in the car there would be a warning light but the fan fuse would likely be blown which would result in a roadside assistance call and tow and a very dissatisfied customer.

On a related note I suspect you have not lived in an area that can experience ice storms. After one of these the ground is littered with broken twigs and bigger debris (like entire trees). So much so that once in a suburb of KS MO after a huge ice storm in early 2003 when I turned on to a little used dead end street to turn around a front tire picked up a twig that fall off and somehow got caught between the brake rotor and brake splash shield. What a racket. I finally managed to free the thing by reversing the car and cutting the steering wheel first one direction then the other. Another time a rock got caught and the screech was unbearable. Zombie fingernails on the blackboard bad. I had to remove the front wheel/tire and pry the shield out a bit to let the rock fall free.

"02996ttx50

really!? i am fairly certain (!?!) mine doesn't.

up4speed

Can you please do me a favor and start the car cold, then physically look at it?
I would really appreciate it. I'm trying to get a pattern here, but I'm having trouble.
At this point the info that makes the most sense is Macster's post. It definitely explains the varied responses.

rmc1148

I would assume yours has the fuse in place that Macster mentioned.

"02996ttx50

i'd be happy to check it again tomorrow as i just folded it up for the night. but I'm confident it comes on only once the engine comp is a certain temp. ( edit: but i can't say it isn't running all the time the car is though... hmm.

up4speed

It sure sounds that way

Thanks!
I guess we are up to the point where the pattern seems that some cars have the C5 fuse installed and others don't. That's why we all have different stories on how it works. I'm going to check mine now, just to see, but obviously I'm expecting to find that fuse installed.
Now the question is, how do they decide which cars get that fuse?

up4speed

As I suspected, fuse C5 is installed in my car.

up4speed

I just checked my friends car. He has a 2004 996tt cabriolet.
His fan reacts exactly like mine.
His car was delivered to a Florida dealer originally. Maybe the original destination of the vehicle is the determining factor of whether that fuse is installed or not, depending on climate?
Well at least I'm confident that my car is "normal" at this point. I'm still definitely curious to know porsches' logic regarding the installation of fuse C5.

Daytonaman

Interesting fan discussion. My 05' has the c5 fuse, however, the fan has only run once after a hot shutdown. Car has a tune and the fan never runs hot or cold. There is no faulty parts in the fan circuit that I can determine. It has been said here that some tunes affect or delete the fan function. I would like to have the fan operate normally as currently I use a floor fan to get rid of the heat after a long drive. I was suprised to hear that a tune won't affect the fan opeation.

mdd

The twig theory of operation sound like made-up nonsense.

Also, per schematics the Stage 2 function mentioned below is controlled by the DME. So a tune could theoretically change the operation but I wouldn't think a tuner would have a reason to alter the operation

Whether Stage 1 works or not is a function of having the C5 fuse installed or not. No DME control possible since it is fed directly from the fuel pump relay. Fuel pump on = fan running.

What's not clear in the schematic is that Stage 1 runs at a lower speed than Stage 2. There must be a resistance someplace in the power feed from the fuel pump relay to the blower relay that is not shown in the schematic.

For the guys with C5 installed, does the fan really run at a slower speed in Stage 1? If so, I'll probably install C5 in my car and take the extra continuous cooling that it provides. I wouldn't want Stage 2 speed all the time though due to the added noise and higher power draw.

From Porsche Technik document:

Two-speed engine 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 longer
than 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.