Radiator Fan run on time

Hi,
Does anyone know roughly how long the radiator fan should run on after the engine & ignition is switched off? It's on a 1.8gti 86 cabby. The fan ran on so long it drained the battery today, I have already replaced the fan switch. It's a 3 wire switch. When it's done it in the past I either unplug the fan or switch to stop and re plug in straight after. cf_emoticons__BangHead:Cheers

Why's the fan running in the first place?

The fan should only kick in if the engine is above normal working temp. Usually because its been sat idling without any air cooling the rad.

If you do switch off with the fan running then it will take longer to switch off because the flow of water has stopped and its now relying on convection of the coolant within the system before it turns back off.

Does the fan switch on and back off while the engine is idling or is it on all the time? if its on all the time it could be a bad thermostat or maybe head gasket, or faulty radiator.

make sure your internal heater fan is turned to cold and the internal fan is off if you carry out any of the above tests. otherwise you could get false results.

Thanks for the reply,
The fan only runs if I sit in heavy traffic for a while. I can't remember it it switches off again while the engine is running so I'll give that test a try when the battery is charged. Thanks!

check if it has the rad fan after-run system, on the rad fan wires check for a random single spade on the red/white wire running off into the loom, if it has one disconnect it the next time the fan runs on engine off and see if that stops the fan.

also have a look around the bay for the thermoswitch, its a single spade brass unit with a yellow collar, it will be on a bracket near the exhaust manifold somewhere, sometimes the spade snaps off and the wire earths itself on engine triggering the system all the time.

but it is normal for the fan to be runnign sometimes after engine switch off regardless of if the after-run system is fitted or not, should only run for a couple minutes or so though

Thanks Rubjonny, I'll check that too!

Mine did this the other week!
I was fortunate to realise soon, as after getting home I went in my back garden about 10 mins later and could hear the fan running, was unsure why it was happening so started her up and turned off and the fan stopped.
I'll have a look to what you mentioned John, but try turning on and then off Rocknrolla, not a fix but might stop you draining the battery.  I've not had an issue since.

Dan

Cheers Dan, nice to know I'm not on my own!
Yomp - I ran the engine at idle until the fan kicked in. It seemed to keep running and running even though the temp gauge dropped. It didn't stop until I unplugged the fan. When I put the plug back it didn't restart again until the temp rose again.
Rubjonny - couldn't find any evidence of an after run system. Couldn't find a thermo switch. The red / white wire goes from the fan straight to the rad switch as does the red/black. 1 x red wire to rad switch and 1 x brown straight to fan. 13.3VDC on red /black when fan runs and 7VDC on red/white. Fan part number 881 082 143
Maybe I've just sh*t out of luck and fitted a dud fan switch!

Sounds like the radiator fan switch is sticking but did you say you've replaced that?
There's no fancy relays between the switch and the fan. Its just hardwired picking up a permanent live from the fuse board wired in series with the fan and then out to an earth on the battery.

Yeah I replaced the fan switch last year when I had the engine out, come to think of it I'm fairly sure it's the second one I've installedsince I've owned the car and problem never seems to disappear. Pretty frustrating really! I have considered installing a relay switched from the ignition to stop it running on but that does seem like admitting defeat! cf_emoticons__BangHead:

yeah sounds liek duff thermoswitch, theres nothing complicated about the system you have 12v into switch then 2 wires from switch to fan.

new higher quality switch I recon

Maybe the fan motor is pulling too many amps which is making the switch run hot fooling it I into thinking the coolants hot.
Bit of a long shot though as I would expect it to blow the fuse instead.