Porsche Enthusiasts Club Forum

Could anybody please tell me where to fnid the sensor or switch that causes the fans to cut in, mine are running all the time from the moment you turn the ignition on. I'm assuming that the connector has come off or the temperature sensor is faulty but I'm open to suggestions. The only up side to it is that it's better than them not working at all!

In true 928 fashion, I'm afraid it's not as simple as a single switch/sensor.

The fans are controlled through a combination of signals from the radiator temp sensor (low down, left hand side of rad), the air intake temp sensor (at rear of intake sticks up with 2 pole connector attached), the fan output stages (heat sinked unit on slam panel at front of engine compartment, RHS) and finally the control unit itself (sits under humped carpeted cover beside passenger seat).

I think there's also a temp switch for the transmission oil...

The wsm has a comprehensive section for checking all these items - it's honestly too much to post here and relies on a number of diagrams to show correct pins of connectors etc.

Handily the sensors can all be tested at the plugs connecting to the control unit under humped cover.

Procedures are in section 19-22 of wsm, "troubleshooting engine cooling". If you don't have wsm then at least you can point your garage to this section (assuming they have a wsm, which of course any decent place claiming to look after 928s will have!)

What have I let myself in for?

Lee you needn't worry.

The 928 is sophisticated but it is a very "logical" car in the meticulous way in which it's engineered.

Helps to have a workshop manual, as well as the thorough service info publications produced by Porsche for each year which contain detailed troubleshooting info.

Failing that Rennlist is a fantastic source of knowledge/help.

Another good starting point for tips is:

http://www.nichols.nu/tips.htm

OK I've read the service information sheet for MY87 cars which introduced the electronic fan control.

Try this test:

With cold engine, ignition on (and presumably both fans on full), what happens if you pull off one of the connectors to the air intake temperature switch (sticking out of back of intake manifold at windscreen end)?

Please report!

Stratfordshark thanks for the knowledgable advice once more, I do have a WSM but I'll try your quick test first if it does it again, spookily I didn't use the car for a couple of days and all seems fine again now! Didn't come on with ignition but were singing away when I got home?