Diagnosing radiator fan won't start

[H286]

yes so there are 3 temperature sensors: 1 for the telltale, 1 for the ECU, 1 for the fan control

Fan Control sensor



ECU (blue) tell-tale (slide on connector)

[Ricky352]

My fan also does not seem to be cutting in on my 8v GTE. I'm assuming it should have cut in by the time the digi dash thermometer is into the 4th segment.

I've tried to check for a blown fuse, but going by the diagram the section where the fan is shown does not have any metal connectors in it to grip a fuse? Horn does work.

Would it be worth buying some sensors and switches? Fan switch on ebay is only £8.

Radiator Fan Switch SNB869 Lucas 1341018 90340497 Genuine Top Quality Guaranteed | eBay UK

[Pigeonrat]

My fan also does not seem to be cutting in on my 8v GTE. I'm assuming it should have cut in by the time the digi dash thermometer is into the 4th segment.

I've tried to check for a blown fuse, but going by the diagram the section where the fan is shown does not have any metal connectors in it to grip a fuse? Horn does work.

Would it be worth buying some sensors and switches? Fan switch on ebay is only £8.

Radiator Fan Switch SNB869 Lucas 1341018 90340497 Genuine Top Quality Guaranteed | eBay UK

I'd guess you've probably investigated by now but as is suggested above, you can test the fan motor by bridging the two connectors going to the radiator switch (a blade fuse would do). If the fan powers up with the ignition on the motor and wiring is fine and it's likely* the switch. If not, try making up a couple of jumper cables to the fan motor - if it works, it's a wiring fault, if it still doesn't it's the motor. Certainly by the 4th segment on the dash the fan should be on, or nearly so.

* Cooling systems can be funny things - could be a clogged radiator, wrong thermostat, air lock, anything. I have a 944 (for my sins, they are not as good as folk would have you believe TBH) and had an absolute nightmare with the cooling system. The thermostat failed open one autumn so I replaced it. Thereafter, come the next summer, it would start to creep up very gradually even at speed on a motorway and then suddenly just run away with itself, and there was nothing you could do once the temperature started to run away - it would just dump all its water all over the road and the only question was whether it took two minutes or five minutes. Fan was working fine so far as I could tell but it didn't help. I replaced the radiator, water pump, fan switch, fan relay, flushed it to death, temporarily bypassed the heater core, bled it literally dozens of times - not easy on those as the expansion tank is not at the top of the system and the pumps are crap - and tried three new thermostats. The solution? Everyone in the UK, including Porsche themselves via their dealers, were supplying the wrong thermostat. "Oh, it supersedes" - no, it doesn't. I rescued the original one from the rubbish pile, cleaned it up and found the temperature stamped on it was 3° lower than any of the new stats. I finally found the right one on US eBay just by luck, imported it at some expense, fitted it, fine ever since. My point is I either had three duff Wahler/genuine Porsche stats in a row - unlikely - or that measly 3° discrepancy was enough to let it run away with itself and boil over every single time. Cooling systems are weird, so check everything, and don't assume a new part is right!

[Ricky352]

Interesting. I'll maybe try bridging the two connectors going to the radiator as you have suggested to see if wiring could be at fault. I have replaced the switch and tried wiring the fan directly to the battery, which worked. So I'm going to rule out faulty fan, switch or fuse. Going now to see if I can order a new thermostat too as apparently they're only about £15. Will keep this updated. Thanks for the info.

[Ricky352]

Got a thermostat delivered for £20.50 and it has made a difference. The temperature gauge still goes into the 4th segment, but only for maybe 5 seconds under normal driving, before going reassuringly back into the 3rd segment. To be honest though sitting in traffic it did stay on the 4th segment for a lot longer than this until the road opened up again. Someone told me that the thermostat only opens fully at 107 degrees which is well into the 4th segment. Anyway I'm much happier since fitting the thermostat and will run it like this for a while and see how it goes.