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A few days ago car would not start - battery completely drained. Hooked up jumper cables from another car, as soon as we hooked them up, large fan on radiator started to run full speed. ( Car had been idle for at least 24 hrs at this point ) It seems this is what drained the battery.
Dealer tells me I need to replace the entire large fan motor on radiator ( $463 )
My question is should I seek another opinion ? Could this be some temperature sensor gone bad that is triggering the fan to come on ?
Currently I have to disconnect the battery when I stop the car as the fan continues to come on randomly and erratically.
many thanks
Thomas
 

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That is possible but I'm not sure why they would be on if the engine is off. The engine coolant temp sensor was a common failure on older cars, perhaps your car is the start of the newer ones failing or a fluke. The best way to check is to first, check for any error codes. Then datalog the engine coolant temp sensor value and see what it reads. If it's ambient when the engine is cold it's right. Then watch for it to warm up.
 

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Discussion Starter #3
Thanks for those ideas. I do have one error code currently : Fuel Temperature Sensor is reporting an "internal failure". Not sure if that could be related though
 

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Fan running when not required

I had a similar problem
On my 2006 jetta tdi when it was under warranty. Dealer changed coolant tempature sensor & haven't had the problem since.
 

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Update on this situation : the main engine fan has been replaced and the problem has gone away. They told me that the fan actually had a short in it which was why it was coming on and off eratically like that.
 

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A few days ago car would not start - battery completely drained. Hooked up jumper cables from another car, as soon as we hooked them up, large fan on radiator started to run full speed. ( Car had been idle for at least 24 hrs at this point ) It seems this is what drained the battery.
Dealer tells me I need to replace the entire large fan motor on radiator ( $463 )
My question is should I seek another opinion ? Could this be some temperature sensor gone bad that is triggering the fan to come on ?
Currently I have to disconnect the battery when I stop the car as the fan continues to come on randomly and erratically.
many thanks
Thomas
I have the exact same problem now and I have had this problem before. I have to disconnect my battery to prevent the battery from being completely drained.
This happened to me a year ago after driving on salty roadways then in the rain. I did a few things to try to fix the problem and one of them worked, but I am not sure which.
First I searched around in the fan for the relay and gave the motor, and area where the relay is a few good bangs with my hand. I also when to the fuse box to see if I could find the fuse for the fan ( I found it, but it controls multiple things in the car) and I unplugged then reseated it. I then figured the salt might be getting into one of the connectors and creating a short, so I sprayed water into the fan area in front and back when the motor was warmed up. I did this to see if it would remove any salt that might be in the connections.
Finally I bought a Fan Relay on Ebay for $50 and by the time it got to my house, the problem was gone.
It's Winter time here in NJ and the roads have been salted for a month now, so the problem is back. I will be back under the hood again very soon to try these things again and see if they work...the spraying of water into the radiator didn't work this time, so on to the fuse box and a few good bangs on the motor assemblies.
BTW - I have found through many years of experience that a good rap with the back of a wooden screw driver fixes many problems...It might work on people too ; )
 
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