M3 aux fan
 

I dug the M3 out of its garage spot over the weekend. I think the last time I drove it was last April (inspection sticker is from 8/19). Anyway, my daughter and I drove it around for a while and other than a dead battery it seems largely fine. I may have mentioned this here before, but for the past few years its had an issue where the aux fan runs constantly - makes the car sound sort of like a vacuum cleaner. They replaced the whole fan assembly last year and it seemed to be working fine at the time, but over the weekend (which wasn't particularly warm), the fan came on and stayed on after a few miles. Any idea here?

Thanks!

It will run for AC. It may run at full speed if the clutch fan isn't working well.

It's also possible that the temp switch in the radiator is bad.

If the clutch fails, the fans have a propensity to shed their blades and wreak havoc on the surrounding hoses and components

Depends on how it fails, of course. If the aux fan is running on high, it's likely failed to unlocked rather than locked.

Thanks, this is helpful!

They replaced the fan clutch yesterday. We'll see if that fixes the issue.

Was there any diag, or was replacing the clutch cheaper than diag?

Not sure - I'll find out later today what the deal is.