Aux fan runs at full speed as soon as I start moving and turns off when I come to a stop

[Nisaja]

Hey guys. Basically the title!

2012 E89 20i.

Prior to this I've only heard the fan when I'm pushing the car.

Today, when not moving, the fan is almost silent, but as soon as I start moving they go on full speed. It's really loud. Kinda worries me.

It turns off when I get on the freeway. Comes back on when the speed drops to about 20-30mph. Turns off when I come to a stop or if speed is below 5mph.

Never seen this behavior before. What could this be?

 

[B21]

Could be a faulty water temp sensor, or a coolant pump related issue…

With these puppies first port of call is a decent fault code reader..

I assume you mean the engine fan not the HVAV fans?

 

[Nisaja]

Could be a faulty water temp sensor, or a coolant pump related issue…

With these puppies first port of call is a decent fault code reader..

I assume you mean the engine fan not the HVAV fans?

Yes it's the engine fan. The oil temp was in it's usual position. Didn't notice anything out of the ordinary. Just that the fan was running at full speed.

 

[B21]

Oil temp is a severely lagging indicator of coolant temperature…car will boil over long before oil moves substantially..

My guess is coolant temp sensor has gone rogue but without some diagnostics you are fumbling in the dark..

 

[Nisaja]

Oil temp is a severely lagging indicator of coolant temperature…car will boil over long before oil moves substantially..

My guess is coolant temp sensor has gone rogue but without some diagnostics you are fumbling in the dark..

Thank you so much. Is the car drivable? I have to do about 100 miles today. I'll unlock the OBC and keep an eye on the coolant temp. Ah but it's probably not giving an accurate reading.

 

[B21]

Oil temp is a severely lagging indicator of coolant temperature…car will boil over long before oil moves substantially..

My guess is coolant temp sensor has gone rogue but without some diagnostics you are fumbling in the dark..

Thank you so much. Is the car drivable? I have to do about 100 miles today. I'll unlock the OBC and keep an eye on the coolant temp. Ah but it's probably not giving an accurate reading.

No idea I wouldn’t drive the car till I resolved the issue..