I installed a new genuine BMW auxiliary fan after my old one crapped out (code 35). The new one is incredibly noisy and annoying the hell out of me. It runs most of the time even on mild days with the A/C off.
I considered just pulling the fuse since I hadn’t even noticed the old fan had crapped out. After I saw the code, I started paying more attention but the only effect I saw was the A/C didn’t work as well at idle. And that was during our recent hot spell, with temps around 90 F.
I found the 50 A fuse behind the glove box but it is a bit tricky to remove so I backed out.
I couldn’t find any info in WDS or TIS on when this fan is supposed to stop and start so I did some checking and I am now wondering if the aux. fan isn’t actually the “main” fan and it is normal for it to run most of the time, just that now I am hearing it.
What I found was the aux fan comes on (A/C off ) when the rad-out temp (ROT) gets to ~72 deg C and it doesn’t switch off until the ROT gets down to a very low ~40 deg C. So once it’s on, it can run for a long while, especially around town. The only way I could get it to turn off idling in the driveway with the ambient about 22 deg C was by spraying into the fan with the garden hose.
I used the fan activation function in AE Scantool to force the fan to run at 30, 60, and 90% speed and estimated the fan was running about 40%. That was surprising because judging by the noise, I thought it was running flat out.
I read the engine-out temp and the rad-out temp with Scantool and confirmed them with an IR gun so the two temp sensors seem to be OK.
After the fan shut down at 40 deg C, it didn’t take the ROT long to get back up to 72 deg C and the fan to restart because the clutch fan is doing virtually nothing. I could stop it easily with a newspaper and it was hardly moving any air. I suspected the clutch was bad so I replaced it it made no difference. It still free-wheels at normal temps at idle.
TIS says the “fan coupling” (which I assume is the clutch) “switches on” at 95 +/- 4 deg C and “switches off” at 60 deg C. So it seems to me the electric fan does the cooling at city driving speeds, air from the car’s movement does the cooling at highway speeds, and the clutch fan only kicks in when things get too hot. This seems to fly in the face of conventional wisdom.
So either the aux fan normally runs a lot and I just hear it a lot more now, or the electronics of my new fan are bad and it is misinterpreting the PWM signal from the DME, or my rad is plugged and the rad-outlet temp is higher than it should be (but I am having no overheating problems.).
Anyone have any any insight?