Firstfives.org

I realized when looking at my car that I do not believe that the Auxiliary fan has ever worked on this car (80 528i). Ive done a few tests to see if it would turn on normally, whether through hot coolant temps or with the AC, neither make it turn on.

The fan spins by touch. But, the connectors going to the resistor look corroded pretty bad, especially the hot.

Ill take the multimeter to the leads going to the resistor and see what shows up. Ill also replace the connectors and test it, maybe check the relay also.

But, if the thing is bad, how do I determine which replacement resistor to go with? Looks like theres two possible, either Bosch or Magna.

Also, I dont believe Ive replaced either of the radiator switches. I can see one, but is there two? Looks like Ill be testing those out also, but seem cheap enough to just replace but seems odds of them failing is little.

I've only seen Bosch on E12s, but regardless, they are cermaic with screws and the Magna have a finned aluminum body with pigtails.

A 528i should have two switches, one in the pipe that kicks upwards that the lower hose goes onto and the other in the tank slighly higher.

Fan relay okay ?

I assume one of the "straggler" relays is the aux fan relay. I yanked both out, and tested them in the horn relay, and both worked as the horn gave a good honk.

Next step was to yank off the driver side grill portion to get at that resistor. I sprayed the heavily rusted screws that hold the leads to the resistor. After letting it sit I went and checked on it. I gave a little tug to the lead connectors gently and noticed that the resistor flexed in the middle...

I pulled it gently from the metal bracket holding it in and the resistor had cracked in half it looks like many years ago. So, Ill be ordering one of those up now.

Ok, so I replaced the Aux fan resistor last night. Unfortunately I stripped out ALL the screws holding that thing in place, they were all rusted out bad.

Ive yet to test voltages to that resistor, but Im trying to clarify what will trigger this fan. From what Ive read, there are at least 2 things that will turn it on. By setting the climate controls to Cold, which is A/C which should start that fan running, and from the coolant temp sensors when those reach a certain temp.

Well just for fun I turned the climate controls to Cold and the fan didnt start up. Ill warm the thing up later today and see if that does it. My AC doesnt work in this car, not sure what the fault is there. But, if I turn the CC to cold, and turn the fan on, the blower inside the car does go so Id say the switch for that is fine.

Ill test out the two switches mentioned in the first reply also, see what they are reading.

You understand it correctly. When the A/C compressor is on, the fan should be on at low speed, thru the relay. I don't have the wiring diagram handy at the moment, but I think when it's switched on thru the temp switch in the radiator, on low speed, it is just thru the switch, not thru the relay. But easiest way to test it is to pull the wires off the switches and short them together and see if it runs. There's also a diode in the circuit that could prevent it from coming on when the A/C is on, but usually they fail closed, not open. High speed is switched only thru a temp switch and thru a relay. One warning here, don't try and use a glass fuse for the Aux fan, the fuse link doesn't melt, but the solder inside it does. Also, that fuse holder location is prone to melting the plastic supporting it and often has to be bent back into shape and in extreme cases people have run an external fuse or kludged in an ATO type fuse.

The fan switches in the radiator can fail, but a marginal radiator can also create problems. Water can flow slowly enough thru there that there while there isn't enough to cool the engine, what water is getting thru is cool, so the fan won't turn on.

Ok, so after getting underneath this car I was able to bridge the two wires for the sensor together. A little spark and it spins like a champ.

I figured testing with my A/C wouldnt be my best choice since I know the A/C doesnt work. Ill leave that for another thread.

Its still cool up here in WI, so gonna have to wait a while for the real heat to come and warm this car up. While Im waiting for my temp needle to bounce, Im sure that will get the gears turning again to get into that cluster and replace/fix the cracked speedo gear, broken drive light pcb and test the low gas light.

After changing a few things, and some new radiator fluid I decided to see if I could test this out some in the heat. I have a temp gun and checked both sides of my radiator, and the right side with the sensors is only about 120F, the drivers side was 195F. I had replaced the water pump, thermostat cover and housing fan and clutch and radiator previously. The radiator was used, but seems to work fine. As mentioned previously in this thread http://www.firstfives.org/bboard/viewto ... highlight= it seems this car might just not get hot enough.

I can always drain and flush. This would give me the opportunity to yank the radiator, test the temp sensors, etc. Just not sure if its worth all that trouble.

The fan works but just seems maybe this one doesnt get hot enough at the sensors.

While carefully monitoring the engine temp, put a piece of cardboard in front of the radiator to block airflow to heat it up. You can test it that way too. Just be sure to keep an eye on things and not overdo it.