Engine Cooling Fan Conditions

[David N.]

Does anyone know the exact conditions for the engine compartment cooling fan to activate? My car has a tendency to run a little warm (95 degrees Celcius according to engine coolant temp diagnostic), but I took it for a spirited run in the mountains today and it was hitting 105 and I noticed the cooling fan still wasn't turning on (this was driving between 30-60mph). The fan came on going home when I was at 94 degrees on the freeway at 80mph. If it uses the coolant temp as its condition, doesn't seem like it's being very consistent.

If it isn't activating consistently, is there a common sensor problem or something that would be to blame? Thanks guys, I tried searching the forum but wasn't having a lot of luck.

-David

Ocean Blue 2000 S

[MNBoxster]

Originally Posted by David N.

Does anyone know the exact conditions for the engine compartment cooling fan to activate? My car has a tendency to run a little warm (95 degrees Celcius according to engine coolant temp diagnostic), but I took it for a spirited run in the mountains today and it was hitting 105 and I noticed the cooling fan still wasn't turning on (this was driving between 30-60mph). The fan came on going home when I was at 94 degrees on the freeway at 80mph. If it uses the coolant temp as its condition, doesn't seem like it's being very consistent.

If it isn't activating consistently, is there a common sensor problem or something that would be to blame? Thanks guys, I tried searching the forum but wasn't having a lot of luck.

-David

Ocean Blue 2000 S

Hi,

The Engine Compartment Purge Fan is triggered by the DME control module as a function of the engine temperature, engine compartment temperature and vehicle speed. There are several vaiables involved, so you may not find a discernible pattern for it's operation.

The issue may be a bad Engine Compartment Purge Fan Relay. It is #8 in the #2 Relay Panel (in the Trunk). The Relays are set in two rows - Top Row - #1-6 (L-R), 2nd Row #7-12(L-R).

A fault (P1674) is detected and stored if the engine speed is greater than 80 rpm and the battery positive voltage lies between 7.5 Volt and 17 Volt.

You can check the relay with a multimeter (always a digital one) as follows:

• 1. Connect multimeter to fan relay (connection point 8 in the rear) terminal 30 and ground.
  Display: approx. 12 V. If nothing is displayed, check fuse B4.
  
  2. Connect multimeter to fan relay terminal 86 and ground.
  
  Display: approx. 12 V. If nothing is displayed, check the DME relay.
  
  3. Check the fan relay. On the relay base, jumper terminal 30 and terminal 87 with a test cable.
  
  If Fan starts: Relay defective

Hope this helps...

Happy Motoring!... Jim'99

[David N.]

Thanks for the advice, I went in today and started testing, here's what I got:

In conditions where the car was idling at 0mph, coolant temp at 93 degrees Celcius, the following values were on Relay 8:

85 - 4V
86 - 13.5V
87 - 13.5V
30 - 0V

I shorted 30 to 87, fan did activate (which kinda figured cuz the fan does indeed work just not at the right times). Upon seeing 0 at terminal 30 first, I checked the B4 fuse, but it seemed to be fine. So I'm guessing at this point it's a bad relay. Anyone know what values at terminal 85 and 86 should cause 87 to close with 30? I guess they are cheap enough to replace and see, but given the nature of the compartment fan, I'm going to have a tough time ascertaining whether or not it's fixed outside of going on some spirited driving again.

BTW, it says '53' on top of the relay. Is that all I need to identify it for replacement?

[MNBoxster]

Originally Posted by David N.

Thanks for the advice, I went in today and started testing, here's what I got:

In conditions where the car was idling at 0mph, coolant temp at 93 degrees Celcius, the following values were on Relay 8:

85 - 4V
86 - 13.5V
87 - 13.5V
30 - 0V

I shorted 30 to 87, fan did activate (which kinda figured cuz the fan does indeed work just not at the right times). Upon seeing 0 at terminal 30 first, I checked the B4 fuse, but it seemed to be fine. So I'm guessing at this point it's a bad relay. Anyone know what values at terminal 85 and 86 should cause 87 to close with 30? I guess they are cheap enough to replace and see, but given the nature of the compartment fan, I'm going to have a tough time ascertaining whether or not it's fixed outside of going on some spirited driving again.

BTW, it says '53' on top of the relay. Is that all I need to identify it for replacement?

Hi,

The relay is just an ordinary SPST automotive relay with a Coil rating of 12VDC, 160mA, 400 ohms.

SPDT Relay : (Single Pole Double Throw Relay) an electromagnetic switch, consist of a coil (terminals 85 & 86), 1 common terminal (30), 1 normally closed terminal (87a), and one normally open terminal (87).

When the coil of the relay is at rest (not energized), the common terminal (30) and the normally closed terminal (87a) have continuity. When the coil is energized, the common terminal (30) and the normally open terminal (87) have continuity.

The diagram below center shows the relay at rest, with the coil not energized. The diagram below right shows the relay with the coil energized. As you can see the coil is an electromagnet that causes the arm that is always connected to the common (30) to pivot when energized whereby contact is broken from the normally closed terminal (87a) and made with the normally open terminal (87).

The Dealer Repair manual does not give the specific terminal values. But, since the relay is pretty cheap, $5-$7, I'd simply change it, they do wear out. This price would be for a standard Bosch SPST Relay. If you want the Dealer Part, it is part# 141.951.253.B and lists for $16.

Another possibility would be the Temperature Switch for the engine compartment. It might be wise to make sure that it's electrical connector isn't corroded and tightly connected. Here's what the DSM says about this Switch:

Temperature Switch for the Engine Compartment

An NTC thermistor is installed between the intake pipes of cylinders 1 and 2 in order to measure the engine compartment temperature.

The DME control module activates the engine compartment fan depending
on the respective engine compartment temperature and various additional
factors.

But, I'm betting that the relay does the job for you. Hope this helps...

Happy Motoring!... Jim'99

[David N.]

Very informative My Porsche Dealership asking $24 for it actually... I'll try local autoparts.

[RandallNeighbour]

Sunset Porsche in Oregon will have it far cheaper than any other dealership. (800) 346-0182

[David N.]

Thanks RN, just ordered it now.

[David N.]

Yeap, I think it was the relay. I put in the new one and the fan seems to be coming on a lot more often, specifically when I'm idling at coolant temp 96 degrees C or so and above. I think the car still could run a little cooler, but it's good to know it's not the compartment fan not doing it's job.

BTW, new relay from Sunset was $13.

Thanks all for the input.

[dragonflyoh]

I have looked in several places and the one condition that I have not seen is the fan running while the engine is running at 180, but it stops when the engine is turned off. Restart the engine and the fans operates. Any ideas would be appreciated.

[thstone]

Originally Posted by David N.

Does anyone know the exact conditions for the engine compartment cooling fan to activate?

Here is how the engine compartment fan works;

Engine Compartment Purge Fan
To reduce the temperature of the engine compartment, a fan actuated by the DME is installed behind the ventilation grille of the passenger side rear fender vent.

If the fan is active, fresh air is fed into the engine compartment. There is a temperature sensor mounted in the engine compartment to provide temperature input to the DME.

Standard Operation:
1. With engine running or ignition on:
If the engine temperature is higher than 102° C and the engine compartment temperature is higher than 60°C, the engine compartment fan is switched on for 30 seconds by the DME control unit and the engine compartment is thus ventilated.
2. With the engine off and vehicle is stationary:
If the engine compartment temperature is higher than 60° C when the engine is switched off (ignition off) or if the engine stalls (engine speed: 0 rpm), the engine compartment fan is switched on for 20 mins.

Note: If the engine temperature has not dropped below 80.25°C after the engine compartment fan has been running for 25 seconds, a fan fault is registered and the coolant level warning lamp is activated (flashes).