Cooling Fans Running On

[James_M]

Afternoon All

I'm just back from the Prescott Open Classic with a few other R19ers (great day as always) but I'm having a problem with my car. It's actually a 968 but everyone on here always seems so helpful that I thought I'd chance my arm.

The cooling fans run on after the engine is shut down, they always have as they should. But now they are not always stopping, this has drained the battery once (and I didn't realise since I often walk away from the car once it's in the garage with the fans still running) and in fact ruined the battery because I didn't go back to the car for three weeks. There's also some evidence that the fans are coming on of their own accord when the car is stone cold.

When I found the car with a completely dead battery yesterday I couldn't get into it because there wasn't enough juice to power the lock motors (I thought the driver's door lock operated manually if needs be but apparently not). The AA man however played an absolute blinder. It was the first car he'd come across where the door fit was so tight that he couldn't get his wedges in to pry the door open a few mm (now the only technique the AA will try) and he was very impressed with the overall build quality. Anyway, what we had to do (in the confines of my tiny garage) was jack the car up with a combination of my low level trolley jack and his standard trolley jack (the AA jacks will not go under a 968 Sport or Clubsport fact fans) so he could crawl under the car where he could just about get the terminals of his booster pack onto the starter motor terminals. This energised the locks and we could get into the car. As soon as he got power to the car the cooling fans came on despite the fact that the car was stone cold...

I'm currently having to stop the fans by taking the relay out when I park the car up and I've ordered a new (expensive) relay but how likely do we think it is that that's the culprit?

All help gratefully received and I'll see you at Bedford with or without fully functioning fans.

Cheers

James

 

[Masher]

Sounds like a thermostat sort of issue to me but I am not technical enough to suggest how to fix it.

Look forward to seeing you at Bedford,
Mick

 

[pauljmcnulty]

With the 944 it's the rad switch 99 times out of 100. The relay is expensive (£130 when I last asked), and it's very unlikely to be that.

The only time I've heard of the relay being the culprit was my own, and that was the fuse box lid letting in water. I got a used one from Alasdair, as they just don't tend to fail so an old one is a pretty safe bet.

 

[chrisg]

Assuming the wiring system is the same on the 968, there's only two trigger points for the fans to work:

1. Radiator embedded thermostat - two temps and two speeds for the fans (88c & 100c IIRC).

2. Switching the aircon on - triggers low speed fan running.


On the basis that your 968 may/may not have AC, I would suggest its almost certainly the thermo switch in the radiator.


You'll have pull various bits out of the way to get at it, including the undertrays and drain/ change the coolant. It is a relatively straightforward job though, given the nearly identical underbonnet architecture of the 968/944.

Give me a ring or drop me an email if you need help:

chrisgrahame@yahoo.co.uk

07540 193874

 

[zcacogp]

Yeah - wot Chris sed.

Audi's and VW's of this era commonly had the same problem, and it was always the thermoswitch in the radiator. It's a little brass housing with some bellows inside, filled with wax. This expands when it gets hot and connects two terminals which turn the fan on. The bellows can fail and this usually leads to the fan not turning on at all as the contacts aren't made, but can cause the contacts to short out intermittently and hence the fan to work erratically. I am guessing it is precisely the same arrangement in the 944/968 with precisely the same cure (replace the thermoswitch).

A new switch always used to be about £7 or £8 on a Mk1 Golf. I guess they may be a bit more for a Porsche. []


Oli.

 

[craiginuk]

Think I paid around £21 from OPC. If it's the same as 944 there might be 2 options to choose from. 2 wire or 3 wire.

 

[James_M]

Thanks for the advice everyone.

The relay was the AA man's suggestion but based on what's been said here I've cancelled my order for a new one; OPC Exeter were excellent as always.

The car also needs an alternator so I may wimp out of attempting the switch myself and have it and the alternator replaced at the same time.

Thanks again

 

[Eldavo]

There are 2 ways to change the thermometer switch depending how manly you are.

One way is to drain off a couple of litres of coolant until the level is below the switch and then replace it. The other method is to try and remove the switch from a full system and try to replace the new one before you get water boarded with coolant.

The second is the quick fix manly way, then top up the coolant and off you go. The first way is the way you'll do it if you ever have to do it again after realising the second way isn't much fun at all actually.

 

[Masher]

Nicely put! That is the sort of practical advice we all need! []
Mick

 

[ChasR]

I would go with the rad switch. From memory they are not mega money from Porsche.

 

[Bob]

Sounds like a very determined AA man - well done to him.

The problem certainly sounds like the temp switch in the radiator, mine did the same a few years ago.

 

[kdp]

When I replaced mine I opted for method 2 using the quick replacement procedure, but it took me so long to actually get the thing in that it turned into a much messier version of method 1!

I would recommend emptying a few litres of coolant out first because unless you locate it in the first few seconds panic sets in and you realize you haven't saved any time after all.

 

[ChasR]

Before you go out and buy the temp switch I would see what happens if you simply disconnect the fan switch. In theory no fans should come on .

 

[os951]

Sounds like radiator thermo switch. Easisest way to change it is to lift left corner of you car a bit higher. Loosen expansion tank's cap to let pressure to escape from system. Then just remove thermo swith. You need a 29mm socket or wrench. Sometimes it's easier to remove from bottom since upper water hose is located just above thermo switch.