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Discussion Starter #1
Hey Guys! I'm relatively new here, just got my beast a few weeks ago, and shes in great shape. i took a spin the other day, it was warm, probably about 95* out, and I was running the AC. Everything was working fine, let it warm up before I left, and took about a 5 mile drive on the highway to get some food. I exited and was waiting at a stoplight when my AC went warm. I noticed instantly, and looked down in horror to see the temp gauge rising to almost the 3/4 mark. the light turned green, and i pulled into a parking lot and shut the car off for about 10 min. I fired it back up after that and drove home the same route, without the AC on, and the temp never went over half. Ive never had the problem since. The one thing i have noticed is that on the highway now, the temp will scoot down to about the 10 o'clock position, and when i stop it will go back to the 12 o'clock position. The only things i can think of are random issues, that may or may not have anything to do with this. The outside temp sensor doesn't work, its stuck at -40, and I cant tell if my aux fan is coming on. Going to go test it later today. would this have anything to do with it? The AC has worked fine since then, and it hasn't overheated. i've already ordered another sensor, and I'm going to be in the process of updating the cooling system ( new hoses, water pump, thermostat, etc..) anything to be concerned about ?

thanks guys. I absolutely love my beast. I've waited my whole life to own an M car, and it does not disappoint. I'm very mechanically inclined, the german electronics just confuse me a bit haha. cheers!
 

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Ok, ill start there, Im ordering the whole coolant system update from Turner motorsports, and i believe that comes in the kit. I know the outside temp sensor may have something to do with the AC getting hot, but what about the temp gauge? there doesnt seem to be a coolant leak anywhere, and the coolant is still full... the car has 94k miles on it, so im doing water pump and t stat and all that stuff..
 

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Research how to read ktemp, my temp gauge swings pretty wildly with only a ten degree change. Ktemp will show you exact actual temps, then decide if something is really broken.
 

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ok sweet guys. thanks for the quick replies. Ill research the Ktemp and Ill check for the aux fan. Does it come on the whole time the AC is on? or i do recall something saying that it only comes on when the AC compressor reads too high on the hi side, it will kick on the fan? also, the Aux fan is the larger fan on the top behind the kidney yes? I also have a smaller fan down low you can see through the bumper opening, that is not the aux fan correct?
 

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Those are great questions that I don't know the answer to.. I do know that my car runs a bit hotter with the AC on, but I'm not sure about when and why the fans turn on. Subscribed though, so I'm sure I'll know here pretty soon. Also, welcome to the board!
 

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Discussion Starter #8
Thank you! I have a feeling I'll never stop learning new little things about this car. So far I'm in love! Haha
 

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The auxiliary fan is the large electric fan in front of the rad. It's quite common for them to fail, especially in hotter climates where they have to work hard. It's critical it works in the ambient temps you are having as it is actually the main fan for moving air through the rad and a/c condenser when stopped and at low speeds. The big belt-driven fan behind the rad doesn't come on hard until the air coming through the rad is at 95 deg C.

The aux fan is activated by the temperature sender in the lower rad hose at around 74 deg C rising. You need INPA or DIS to read this temp. DIS has a good test for the fan. It's also activated by the a/c system pressure and runs faster as the pressure increases. The DME controls its speed by sending a varying signal to the fan motor (there's no relay).

Now you're the proud owner of an M5 (and they are a fun car), you need some way of reading trouble codes! A failed fan sets a 35 (hex) code.

And of course, it could be the fuse, which is a massive 50 amp one that requires moving the glove box to access.

Also it seems to be quite common for the power supply wire to the fan to burn and melt. I'm not sure if that is because it's undersized for hotter climates (and I'd call 95 in May hot), or if they start to draw excessive current when failing.
 

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Don't forget to check for power and ground at the connector. Also check for the 3-4 volts at the signal wire (the smaller of the two power/ground wires)

The fan will always turn on when the AC is on, regardless of outside temp. Keep in mind the 3-4 volts on the smaller signal wire is only present for the first 5-10 seconds when turning the AC on, only if the computer does not see the fan physically turning on, it shuts off power/voltage through the small wire) So you have to test for voltage quickly.

I had a break in the signal wire on one of my previous m5's. I prematurely purchased a new auxiliary fan before testing for power/ground/signal.


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