Hi, I had an overcooling fault, whereby the engine would never reach the correct temperature, with all the normal associated problems, such as ineffective heater etc, this was obviously a faulty thermostat problem.

 

When I went to replace the thermostat, I discovered there wasn't a thermostat fitted ( someone had previously removed it... ), I fitted a new thermostat and all appeared well, correct engine temperature reached, good heater etc, BUT I think I have discovered an underlying problem ( the reason the thermostat was not fitted before ).

 

Now, once the engine heats up, the radiator fans kick in, BUT they NEVER switch off again, the engine needs to be turned off and allowed to cool down.

 

The temperature gauge reaches the halfway mark and stays at that.

 

The engine is the 1.4 16v AUB type with one coil pack and not individual pencils, the radiator has TWO electric fans and the radiator was recently replaced just before I got the car ( fathers old car, so I know for sure it was changed ). W registration year.

 

The engine is 'pinking' once temperature is reached, but not while heating up.

 

I suspect a dodgy tech removed the thermostat previously instead of finding and fixing the underlying fault ... :/

 

Could the radiator thermoswitch be at fault ?, obviously it switches on once a preset 'trip' temperature is reached, BUT is it possible for these switches to fail in an 'on' state ?, I don't think this is the problem however, because the fans don't run when the engine is cool, so the switch must be turning off when coolant temperature drops, when the engine is turned off.

 

I have checked to make sure the air con isn't a problem ( I realise the fans would run if air con was switched on ).

 

I will try to measure the resistance of the thermoswitch ( hot & cold ) and check against specs, but is there something else that could cause the fans to kick in and stay on once the engine has reached operating temperature ?

 

I have tried to include as much info as possible, any help would be appreciated, thank you

 

 

The thermoswitch might be sticking 'on', but I'd imagine it's not very likely as on these cars it isn't carrying the full fan supply currents, just a signal or relay coil feed, so not likely to weld its own contacts. The high-current switching is done by a fan control module which hangs off a bracket on the nearside chassis leg, close to the radiator thermoswitch.  Worth trying another module from a scrapyard I would think. 

 

Firstly though; check wiring to, and connections at the fan control module, looking for corrosion or damage.

Fan control module

 

They're a constant sodding fault on VAG stuff.

 

(There's also the resistors on the radiator fans which fail too)  There's a thread on ukmkivs about fixing them.

Hi, thanks for your replies, I will look into this and check it out, I didn't know there was a Fan Control Module, the workshop manual I have didn't mention it and rather unhelpfully there also isn't a wiring diagram in the book which shows the fan components ( schematics for everything else, except that...:/ ) so it's no wonder I 'missed it'. Back to Google now, see if I can find a pic, so I know what I'm looking for.

 

Cheers

bumping this thread again, I still have the problems mentioned above, I cant find the fan control module and kind of gave up on this problem, but it is a constant thing that I keep thinking about and returning to, I've scoured this forum and google but I cant identify where this fan control module is and 'THE WORKSHOP MANUAL' is rubbish, ( loads of discrepancies and misinformation ) does someone out there have a picture of its location or can give me more detailed info about finding it, please. The sound of the fans going full on all the time once temperature is reached is driving me nuts...thanks

The fan control relay module is very close to the thermoswitch, it's attached to the body next to the PAS pump and is a black box.

Pull the connector off the radiator thermoswitch and see if the fans stay off.

The fan controller is on the pass chassis leg at the front, you may have to remove the battery box to get at it easily, disconnect the multi plug that has lots of thin wires and check for corrosion on the contacts inside, also check that all the wires are good and not rotted away where they go in to the plug, Funnily enough I have just fixed an octavia with the same problem and it was the perm + into the unit that had corroded away, fans would come on and stay on until the battery was flat.

Not sure that your car will have the fan controller. Just looked at wiring diagram for a 2000 AUB and the dual thermoswitch on the rad does directly feed battery 12V to the fan. So, contrary to my earlier reply, it may indeed be that the thermowitch has failed with contacts welded closed.

Not sure that your car will have the fan controller. Just looked at wiring diagram for a 2000 AUB and the dual thermoswitch on the rad does directly feed battery 12V to the fan. So, contrary to my earlier reply, it may indeed be that the thermowitch has failed with contacts welded closed.

 

Mine is a 2000 AUB and does indeed have the fan controller, please explain.

The fan controller was perhaps introduced during 2000?

 

Edit: yep looks like there was a difference after August 2000.

Edit2: after scrolling through hundreds of diagrams, that next version doesn't show it either.

Will have a better look tomorrow on an easier computer.

The fan controller was perhaps introduced during 2000?

Edit: yep looks like there was a difference after August 2000.

It's an elegance so it has a fan controller (since Q3 1999). Unlike the Octavia, neither fan is controlled directly by the thermoswitch.

Thanks for that. :sun:

In that case it's where I, and everyone else says.

Ok thanks everyone, that's very useful, I will investigate further tomorrow morning, thankfully its ideal weather at the moment for doing things like this out on the side of the road ( how I wish I had a garage... ), will report back what I find

I found it, don't know why I couldn't before because its quite a large module ( a lot bigger than it looks when viewing pics of it online ).

Although from above the mounting bracket doesn't look too traumatic to get to, I don't think it can be extracted from above due to its connecting wires being too short to pull it upwards and the cramped conditions due to adjacent wiring looms etc, I reckon it would be easier ( I say easier, but still a lot of work...) to remove it by accessing from beneath the car by perhaps removing the engine protective undertray or by removing the road wheel and then the inner wheel arch plastic cover ( lots of torx head screws ) which would also reveal the windscreen water bottle and power steering pump.

If I'm missing a more obvious and easy way of doing this, I would love to hear about it.

If it was our car, I'd drop the engine undertray off, not much work at all on a 1.2. Dunno what it's like on yours though, but I doubt there's a better way to get access.