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Thread: 1.9 PD Radiator fan running constantly

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  1. 1.9 PD Radiator fan running constantly 
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    There is clearly something very strange going on with my Passat and I'm at the end of my tether trying to figure out what's wrong with it. Coolant temp sensor, thermostat and the sensor at the bottom of the rad are all new.

    The larger belt driven radiator fan is running fast as soon as the engine is fired up until it's shut off. This happens with or without the aircon on. This is preventing the engine getting up to temp which didn't both me too much until today when it failed the MOT on emissions - I suspect due to the test being carried out on a cold engine.

    Does anyone have any ideas on this? It seems a real shame to scrap a perfectly good and usable vehicle for the sake of a misbehaving fan, but unfortunately if I can't get this resolved and through the MOT it's my only option.
     
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  2. Re: 1.9 PD Radiator fan running constantly 
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    engine code or reg no would help for to help you more
     
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  3. Re: 1.9 PD Radiator fan running constantly 
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    It's an AWX. 5 speed manual 130bhp.
     
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  4. Re: 1.9 PD Radiator fan running constantly 
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    Tammy, I don’t want to appear viscous Fan clutch - Wikipedia but do you understand how the “belt driven fan” works?


     
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  5. Re: 1.9 PD Radiator fan running constantly 
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    Apologes, I should have been more specific! I think I know the basics of how they work. As engine speed and temperature increase, the clutch kicks in and increases the fan speed to prevent overheating.

    The problem I have is that from a cold startup, at idle, the fan is running fast enough to be heard with the bonnet closed. In fact it's running so fast that it's preventing the car from reaching 90 degrees. My understanding is that in these conditions the clutch should be disengaged and therefore any movement of the fan should be minimal? I suspect that whatever controls the clutch is at fault hence changing both temp sensors as it made sense to me that one of them, most likely the one in the bottom hose, would be responsible. This has made no difference at all, so I was clearly wrong and am now out of ideas!
     
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  6. Re: 1.9 PD Radiator fan running constantly 
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    The fan itself contains a bimetal strip which controls the fan's clutch, this may be faulty. Just to confirm, the secondary electric fan is not running and you have the air con control set to Econ? If you do a google search for B5 viscous fan you'll find a number of suggestions on how to check them, though admitedly they seem to be more focused on the opposite to your problem.
     
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  7. Re: 1.9 PD Radiator fan running constantly 
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    No you missed it, VISCOUS as in viscous fan coupling, with the engine OFF, can you freely spin the fan? The unit is completely self contained and its sensor is the fluid inside which becomes thicker as it heats up and so drives the fan, when it fails the units fail safe is to stick on so prevent overheating.
     
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