97 E36 M3 Aux fan issues

[BoogieManTM]

Hey all.

I picked up a project e36 m3 on the cheap a few years ago. Have been slowly working on it ever since. I have had some overheating problems, and I discovered the aux fan cable connector was shredded. I replaced the whole aux fan unit and wired up a new connector with bullet connectors soldered to the wires. Replaced the 30a and 5a fuses and went to test everything out by jumping the radiator heat switch connector.. fan turns on high and low when jumped directly, so as far as I can tell, the relay, fuses and fan are totally fine.

Tried running the car for a while to see if the fan turns on.. never turned on even at normal operating temps after running for about 15 mins (even with the AC on) So I figure it's the radiator temp switch is bad.. ended up buying a ecs tuning electric fan conversion (here https://www.ecstuning.com/b-assembled-by-ecs-parts/electric-fan-conversion-kit/e36fndkt6/ ) which replaces the temp switch with an even more sensitive one that should spin up earlier than the stock switch.. no joy. still will not start the fan when the AC is on, or after running the car for a while. I have not finished the electric conversion, just replaced the switch so far.

I hooked up the old switch after replacing it with the fan conversion switch and put a lighter to it for a minute or so.. brass got so hot I could not touch it with bare skin, but still the fan refused to kick on. I'm at a loss for what might be wrong here. Any ideas?

Radiator, water pump, pulley, belts, plumbing and thermostat have all been swapped out earlier in the project, so I'm pretty sure the issue isn't with them.

Could this be a fluid issue? My radiator doesn't seem to be getting very hot, so I suspect the original switch is just toast, and the new one is simply not getting hot. Air bubbles in the coolant preventing proper flow, maybe?

[Eric93se]

So good testing but mixed conclusions. The AC has nothing to do with the fan temp switch. The fans should have come on with the AC, unless its either too cold outside or something else. My thought is there may be some bad wiring between the DME and relay box. Your thought on of the low coolant in the rad is a possibility, if the expansion tank is bad, look inside it there should be a plastic tube running from the top all the way to the bottom, if its not fully there then you need a new one. I'm not sure about how effective your lighter test is but I know the fan temp switch will work better if you wrap the brass with an insulator, I used Styrofoam and duct tape.

[shogun]

Moved to M3 forum

[BoogieManTM]

Yeah, I am aware the AC is not connected to the rad switch. Just being too thorough in stating what does and does not work. I suspect you're right about why the AC isn't kicking on though, it was probably too cold in my garage to kick in.

I got my hands on a refill/air purge tool.. tried it out without flushing the whole system. Vacuum seemed stable, and it drank a fair amount of distilled water (planning on flushing later with a proper mix), about half a gallon. Bled the system again with the bleed screw and let it run for about 40 minutes. Coolant temp in the car got to the far right line, approaching the red.. Fan still refuses to turn on. I touch tested the rad all over, and the right side was definitely hotter than the left, but the brass of the rad switch was still pretty hot to the touch. Manually jumped the switch connector again on high, and sure enough the temp starts to drop back to the middle of the gauge.

For the expansion tank, there is a tube going down under the bleed screw to the bottom of the tank. is that what you're talking about?

It seems like this switch is also bad.. seems unlikely but not impossible. Any other potential problems this might be?

[LockDots]

If the aux fan is still kicking on when you jump the pins at the radiator switch the only thing left really is either a bad rad switch or a pocket of air in that corner not allowing the coolant to warm up the switch enoigh to trip.

Sent from my SAMSUNG-SM-G920A using Tapatalk

[BoogieManTM]

Alright. I picked up an all aluminum expansion tank to match the electric fan conversion and hopefully "complete" my cooling upgrades. I also picked up ANOTHER temp switch, as well as a new coolant level sensor. I'll flush the radiator and block and give it another shot.

Thanks for the help so far. This has been a real pain in the butt.

[BoogieManTM]

conversion completed. properly flushed everything out, replaced the overflow tank, installed the electric fan and controller, filled her up with a proper coolant mix (using the vacuum filler tool) and bled it for good measure once she got warm. the new electric fan is kicking on with it's own temp sensor in the radiator. aux fan still never kicked on, but the electric fan was never letting it get hot enough this time, I think. As a final test, I took my original aux fan rad temp switch, connected it up out of the car and took a map gas torch to it for a few seconds.. it did finally kick on! woohoo!

Must have been air in the radiator that was screwing me over, and my aux fan switch sensors were fine the whole time.

Thanks again for the help!