Auxiliary Fan issue - 08 528i
 

Hello, brand new here. I have 08 BMW 528i that has 117,000 miles on it. Been fortunate and never had any major issues with it. Recently, I noticed that the car was reporting higher than normal operating temperatures when idling using the ultra-gauge. Upon inspection I found the auxiliary fan to be bad, tried to jump it but it would do nothing. I purchased a new fan online and installed. Problem solved, or so I thought. Drove the care my 20 mile commute in the morning, car performed perfectly. After driving almost home though in 95 degree heat, the cars temperature started increasing at a red light. When I got home, I checked and the fan had again stopped.

My thoughts are that I have a bad high speed relay that is not connecting when the car calls for the fan to get to high speed. After the car cools down, you can crank it up and the fan will operate again. Seems that it doesn't work when it is calling for high speed.

Please let me know if I am looking in the right direction or if there is something else I should be looking at. Thanks in advance.

Welcome to the forum. On my 545 the coolant temperature sensor located on the lower radiator hose is what triggers the fan to turn when coolant heat becomes excessive. I believe your sensor is on the passenger side radiator hose, and this could be your problem. Good luck.

so the fan works intermittently. Worked all day today, then when driving home from work it didn't work. A/C does not blow cold air, fan doesn't work. When I got in the car, fan initially started and then went off. Drove 20 miles home with no fan. Came home, let the car cool off for 5 minutes, restarted car and fan worked perfectly.


I'm really confused here. What could be causing this.

check the sensor yet?

I just had the same problem, most likely the sensor. Also your ac needs to be charged, for some reason the cooling system work in conjunction with the fan. After I changed the fan motor and sensor the overheating persisted when in traffic on the test drive. Had the ac charged an all is ok.

I cant locate the coolant temp sensor on my car. I have the new part in hand, but cant find the old one. I am looking on the lower radiator hose (return). it does not appear to be where it is in the diagram. I just have a regular hose there, labeled BMW, no connector. Any ideas?


http://www.realoem.com/bmw/diagrams/i/i/238.png

So i changed the coolant temp sensor and charged the AC with refridgerant. Same results.

More symptoms. Everything works fine in the morning. Once it gets warm in the afternoon, 88+ degrees I start having issues. The A/C quits blowing cool, temps start rising, and the best I can tell, the fan quits working. This thing has me very confused. I have replaced fan, and coolant temp sensor thus far. What would be my next step?

Buzzy,
I have the EXACT same issue and car. 2008 BMW 528i:

1. Low fan speed works fine and everything is good on cool days.
2. If it gets hot out, or after excessive/aggressive driving, high fan speed never seems to engage at stop or idle. When this happens car temp gets hot and AC stops blowing cold air.
I remember what the fan used to sound like on hot days at idle. Haven't heard the high speed fan in a long time......

Fixes I've tried:
1. Coolant flush/fill/auto-bleed
2. Proper AC evacuation/recharge
3. Checked ground and wiring to fan


I too have a new coolant temp sensor replacement part, as I read this could be the problem, and I can verify that the 528i 2008 does not have the coolant temp sensor near radiator hose(s) at the bottom of radiator.

Did you ever figure out the solution to the fan never going to high speed? And where is our coolant temp sensor?

Help! Everyone's input is welcome.
I should add that my icarly OBD app appears to show everything working fine including temp sensors for coolant. Again, the fan works but only low speed. I'm baffled.

Were the hoses broken. If so perform the bleed procedure twice. What brand fan did you use. Have you checked the fuses/relay or fan switch? You need a program to read what is happening to the system but what I have listed should work if everything was working before the swap. The temp sensor should not have needed to be changed if it was working fine before the swap but it is good practice to go ahead and change it with the fan if it is the original.

The coolant system is working great 100% as far as I can tell.
My problem is with the aux fan (OEM). The fan runs on low when the engine heats up or if I turn the AC on.
But the fan never runs on high even on an extremely hot day with aggressive driving and I cant figure out the problem. AC pressure is good and coolant temp gets hot enough. On an 08' 528i this should trigger the fan running on high - which it used to do.