cooling fan comes on randomly

lrb

Member
Joined
Jan 31, 2020
Location
lancashire
TDI
2008 mk5 golf 1.9tdi
Hi

I've had an ongoing issue with my 2008 golf 1.9 BXE engine in that the cooling fan just comes on whenever it wants and usually stays on for quite a while. This is obviously effecting the idle speed and I've noticed my mpg has dropped.

I've had a few suggestions as what it could be and have so far changed both the coolant temperature sensors ( one in the lower hose and the one in the side of the engine). The cooling fan (mine is the single large one) and today have changed the air con pressure sensor.

When the fan comes on it is on full speed that made me think it was something to do with the air con. Hence why i change the pressure sensor.

I am now stumped as what to look at next. If it is something to do with the air con is there a way of disconnecting the system so I can eliminate this or simply leave the air con disconnected (not like we really need it here)

Thanks
 

eddieleephd

Top Post Dawg
Joined
May 27, 2012
Location
Battle Ground, Wa
TDI
2002 jetta Wagon
For some reason you don't think it should be coming on when it does?
My recommendation is to stick a thermometer probe there and a multimeter in the car so you can see what temperature it's at when this happens.
Fan control unit controls the fans and it should be on with the AC...

Sent from my moto g(7) power using Tapatalk
 

lrb

Member
Joined
Jan 31, 2020
Location
lancashire
TDI
2008 mk5 golf 1.9tdi
The fan can come on after the car is running for about 20 seconds. So seeing what temp is when it comes on wont matter. It comes on randomly. The AC is switched off.
 

AndyBees

Top Post Dawg
Joined
May 27, 2003
Location
Southeast Kentucky
TDI
Silver 2003 Jetta TDI, Silver 2000 Jetta TDI (sold), '84 Vanagon with '02 ALH engine
My suggestion would have been to change the Temp Sensor(s). However, you've already done that. A friend of mine had a 2007 VW Eos that had a very similar issue. About 15 seconds after the engine was started (cold or hot), the fans would come on and run. A few times they did not kick-off which resulted in a dead battery. Replacing one of the Temp Sensors solved the problem.

While researching the issue on the Eos, if I remember correctly, I found that the Fan Control Module (FCM) is built into one of the fan motors. On the MK4 models, the FCM was a separate unit mounted on the chassis under the battery.
 

Scooby24

Well-known member
Joined
Jan 13, 2020
Location
Olathe, KS
TDI
2014 Passat TDI SEL
Does your fan come on, like mine does, when it's doing a regen? My last regen lasted 20 minutes.
 

lrb

Member
Joined
Jan 31, 2020
Location
lancashire
TDI
2008 mk5 golf 1.9tdi
I replaced the Air con pressure switch today as someone suggested the air con may be switchi g the fan on. I now notice its not coming on as frequently but still randomly.
Must be something to do with air con but still stumped. Could do with someone with a vagcom
 

eddieleephd

Top Post Dawg
Joined
May 27, 2012
Location
Battle Ground, Wa
TDI
2002 jetta Wagon
Are you using the air conditioning, or the heat?
Many other manufacturers implement the air conditioner when in heat to extract the humidity from the air and allow it to heat quicker.
 

lrb

Member
Joined
Jan 31, 2020
Location
lancashire
TDI
2008 mk5 golf 1.9tdi
Are you using the air conditioning, or the heat?
Many other manufacturers implement the air conditioner when in heat to extract the humidity from the air and allow it to heat quicker.
Doesn't seem to make a differance if i hace the air con on or off or the heater blower on or off
 
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