944 fan prob - temp switch or relay?
 

1988 944S cooling fan behaving strangely. When engine is running, fan doesn't operate, and engine overheats in traffic or when just idling. When engine off, fan cuts in and out as normal for a while after a run. Engine runs at normal temperature when moving.

I have been advised that it could be either the fan relay, or the temperature switch on the radiator. The relay is easy to change, but expensive: £70 or so I am advised. The temperature switch is cheap (£10) but not easy to replace.

So what do I do? Is it obvious from the symptoms that it is one or the other? Can I test the relay in any way? Can I get the relay cheaper: it must be used on other cars e.g. VW?

Thanks in anticipation - Dave

wow, that's an odd one. i would go with relay.

Have you tried bleeding air out of the cooling system? Sometimes a small pocket of air can cause weird temp issues. It's easy to do and doesn't cost anything. Might be worth a shot?

Here's a "how to" if you are not familiar with the process: http://clarks-garage.com/pdf-manual/cool-02.pdf

Yes that was on of the first things I tried, but would an air pocket stop the fan coming on?

I have now tried jumping the leads to the radiator temp switch and the fan works fine - slow speed with the ignition off, fast with it on, the relay clicking away nice and crisp. So I'm guessing that it's probably an intermittent fault on the rad temp switch.

(BTW my 1988 model 944S does not have the three way connector shown in the Clarks manual, just two spade connectors, and only one fan. Maybe UK models were different?)

That is strange your 944S does not have the 3 pin connector. They were only used on the '83-85 944 and the '87-88 924S. Dont think it being a UK model makes a difference as it was switched over when the upper and lower radiator supports (and radiator) were changed over. The 924S uses the early style radiator mount.

I would see about changing the fan switch, its not hard to do really..just a bit of a mess as coolant comes pouring out.

is there a porsche junk yard nearby? i would buy a used good cooling fan relay to test even though you should have an extra one.

It's a crap shoot sometimes between the 2 but I usually start cheap and work my way up!

FAO Dave Boettcher - my 1984 944 also has same fan inoperative symptom when engine is running, but fan comes on as normal when engine ignition turned off. Like you I have bridged the switch wiring which turns fan on. Realise your post is pretty old now, but what cured you 944??? Regards

If its a late model, you can test the relay by jumping the terminals which plug into the temperature switch (this is outlined in the clarks article above). This is a three prong plug which connects to your fan temp switch on the upper radiator. All late models have this connector, so if you are saying you dont have three prongs you are looking at the wrong connector. If you jumper these based on the methodology on clarks and it checks out, your relay is good and you can look at replacing the temp switch on the radiator (because its sending the wrong signals or none at all to the relay).

Make sure you get the same temp as there are at least 3 different temp switches which activate at different temps.

The clarks procedure is pretty clear. Other possible issue are your fans themselves (not the issue since they still run) or the fan resistors near your hood cowling.