Porsche Enthusiasts Club Forum

Hi guys, just picked up an S4 which is a fantastic car. Running well but the cooling fans run intermittently when the engine is cold to the extent that the battery was flat this morning. The fan came on when I shut the car door even though it was very cold this morning.
Any advice on common problems would be appreciated.
Cheers
Paul.

Hi Paul

Could you provide a little more detail on the problem (as well as model year, since some S4s did not have cooling flaps).

You say fans run intermittently. Do you mean they run and stop with key out of ignition? How long do they run for? When do they come back on?

Cheers

Adrian

Hi Adrian, thanks for response. It is a 1990 G and does have the cooling flaps although not sure they work as it has been sat with no battery since June.

Picked it up Thursday and has been running and starting fine although I had noticed the fan kicked in and out from time to time. Last night got back from gym and got out of the car and the fan was running, shut the door and waited and the fan went off.

Went out this morning opened the door and the fan came on which I thought was a bit odd. The dash lights were on but not enough juice to turn over so turned it off and the fan was running again so I believe it was running o and off during the night and flattened the battery.

The question is what would make the fan run on a car that had been stationary all night?
Cheers
Paul

You can check the cooling flaps by watching them as someone starts car - they will run through test cycle.

I am concerned that you have other electrical problems as the fan behaviour is odd in being intermittent. The advice I can give applies to when the fans run continuously, with ignition off.

Try and catch the fans running when they shouldn't. Check that the connector is attached to radiator coolant sensor low down on left side (as you sit in car) of rad. Fans will run if this is disconnected. Watch out for the fans they are powerful and sharp!

If the connector is ok and fans are running, then pull either of the connectors off the air intake sensor at rear of intake manifold. If fans stop the sensor is faulty (cheap, easy fix).

Have you made sure aircon switch not pushed in? Fans will always run with aircon on, but only with ignition on. Similarly even with aircon off have you made sure the HVAC control (below temp slider) is not in left recirc position? This will force aircon/fans on regardless of aircon switch.

Do you know anything of history of car in terms of aftermarket fit of alarms, sound system etc? That is a common source if electrical problems when people splice into circuits at points where they shouldn't. When you mentioned fans coming on when you opened door it conjured up fears of deeper electrical issues than just problem in fan control! Let's hope fears groundless.

The 928 S4 fan control is very smart, but as failsafe it will run fans at full pelt when it detects a failure in any of components in control loop.

Do you have the workshop manual? This has excellent section on troubleshooting any fan control issues. You can purchase copy on CD from John Speake just google JDS Porsche. Best investment you can make in a 928!