Cooling Fan Issues

[iamthewheelman]

Alright so I have an interesting issue. My cooling fan will only work properly when my blower motor is on. Basically if I drive around with my HVAC on all the time I am good but the second I turn it off, the cooling fan won't engage so I overheat at stop lights and in traffic. I start driving and the engine temp emidiately drops back down to normal. I am thinking thermostat or fan relay? I have been into shop key and couldn't really find anything.

 

[iamthewheelman]

no one has any ideas?

 

[paper1122]

Without knowing everything about these cars I can tell you on a previous vehicle I had a bad temperature sensor that told the fan when to come on. I just removed the radiator on my P5 and I know that it does not have this sensor on the radiator.
Just a dumb question, did you check all of the connections to fan? If you did, I would suggest turning on the car, let it warm up and then check to see if you have a voltage signal coming to the harness at the fan. If you have voltage then it's a bad fan, if you don't it is most likely going to be a relay or sensor. I'd be interested to find out what you come up with.

 

[iamthewheelman]

The fan should still be good as it turns on with the blower motor, making me think there is an incomplete circuit somewhere and when the blower motor is turned on the circuit is somehow completed. Both the temperature sensor and the relay are cheap, so I should just replace them and go from there. But your idea for checking seems like a good place to start either way.

 

[paper1122]

Are you sure both fans are coming one? I think one is directly linked to the A/C while the other is for cooling. Please forgive me for asking simple questions, I like to start simple and work to the more complicated.

 

[iamthewheelman]

The bigger fan on the driver side is for cooling, the smaller fan on the passenger side only engages when the AC is on, I know for a fact that the AC fan works normally, and the cooling fan only engages properly when the blower is on.

 

[d0sitmatr]

it sounds like a bad relay.
have you verified the fan doesnt come on at all without the HVAC ?
when I first got my mp5, I thought the same thing as you since my primary fan never came on, even middle of summer with 100+ ambient temps. but it did come on with the AC so if I was driving longer distances I would just use the AC on a low/warmer setting.

but about a month ago, after about a 30 minute drive, when I stopped the car, the fan was on.
Id look into a way to set the temp it comes on at a slightly cooler level (if possible)

 

[i12drivemyMP5]

Doesn't the ecu control the primary fan temp setting? Maybe the ecu isn't getting the required info to turn on the fan? Not sure which sensor would be providing temp info to ecu that isn't working but the gauge is somehow getting info it needs to tell you car is getting hot.....

 

[iamthewheelman]

That is a good idea, my wiring harness is in pretty rough shape lol