Fan won't stop running until the car dies *Please Help*

I just bought a 95 BMW 318i on July 13th and have had no problems until last night. The fan kept running after I shut the car off at a park where I had stopped to eat at and then leave. I was there for about 20 mintues. Seemed really strange, but I started the car up–and it started just fine–drove home and parked it away. When I turned it off the fan stayed on again. It’s not overheating and I had hoped it would shut off by itself after a little longer so that it wouldn’t be dead in the morning.

So This morning I came down to my car to go to work and the fan was off. Good right?–no. The battery was dead–good thing I still have my other car as a fallback.

Came back home…searched online to where the battery was–never thought to look in the trunk :wink: and hooked up the battery charger to it. As soon as I did that the fan came back on, but it would not start. So I let it continue charging for about an hour and came back to it. Tried to start it again and the battery charger would shut off along with the fan, and then after about 5 seconds the battery charger would come back on and the fan would start back up. I have left it charging ever since—been 3 hours now. Speaking of which I’m going to go check it again quick before I post this.

So aparently that killed the battery charger. There is still power to the extention cord–but yeah, car is still totally dead—no lights, no fan, no nothing… + now no charger…

What should I do and why is the fan staying on when there is no sign of it overheating? This is a problem I have never experienced with any car I have had. Please Help.

Any engine will get hotter for a brief time after you shut it off. This is entirely normal.
The temperature will spike upwards because the water pump is no longer circulating coolant and air is not moving through the radiator.

The temp spikes upwards and a coolant temp sensor will activate the fan and keep it running until the coolant temp drops below what the sensor is rated at.
Usually the fan will kick off after 5 minutes or so, depending on a number of factors.

If you’re using one of those hand-carried battery chargers you must always disconnect it before starting an engine unless it’s a heavy duty charger with a boost function.

Those chargers cannot keep up with the amount of current required to operate a starter motor and the charger quit because the safety circuit breaker inside the charger was overloaded and popped open. Hopefully once cooled down it will operate as normal when the points close, but don’t do this too much or the charger will fry for good.

I should have added that if you mean the fan cycles on after turning the car off and runs until the battery is stone dead then the problem could be sticking points in a fan relay or possibly the fan temp sensor itself.

Yeah, the fan runs until the battery is completely dead. Like I said though it’s not overheating. I understand it’s normal to run for a few minutes after the car has been driven. This is not normal by any means though. I just don’t get it. I thought about maybe a sensor–but not sure where to start looking and I don’t want to dump alot of money into it TRYING to find the solution. *frustrating.

OK4450 & OP:

Here is the wiring diagram for the fans. I hope it helps.


I think your problem is in the temperature switch. It looks like it switch the low speed fan on at 91 deg C and the Hi speed @ 99 deg C.

Do you know if the low speed fan or the high speed fan is running?


I wish that did help—unfortunately it’s pretty forein to me. I don’t understand how to read it and what I’m am supposed to learn from that. If I took out the 2 sensors you had mentioned above and took the in to an auto parts shop, would they be able to test them somehow so I would know for sure?

sounds likes it moving at full speed if not faster.

I located and posted the diagram thinking that OK4450 would take a look and chime back in with some advice. The guy really knows what he is talking about. There are times I wished I lived in Oklahoma so he could work on my car.
If the car came into my shop I would use a test light to try to isolate where the power is coming from. It sounds as if either the high speed relay is stuck or the temperature switch is closed.
You could try unplugging the relays one at a time and see if the fan stops. I would start with the high speed relay and see if that stops the fan.
I don’t think that you could rely on a bench test of the relays.

I recieved this response on–posted the same problem to see a few different results.

This is what he said, “Unplug the fan from the wiring harness. You don’t need it if you have the engine-driven fan installed. Then fix at your convenience – probably a radiator fan switch has failed on you. It’s on the upper right of the radiator on the three bimmers I’ve owned/worked on.”

Wouldn’t that make the car overheat? At first glance |I don’t see this as a good idea. I will try out a few of these ideas tomorrow after work and see what I come up with. Starting with yours cause this seems like a bad idea to disconnect the fan. I’ll be back to update tomorrow. Thanks for your help so far–hope one of these ideas solves it.

Thank you for the embarassingly kind words Dartman.
I think you’re right about a relay or time switch sticking.
The diagram would not pull up for me; only the top 1/2" or so. The few BMW diagrams I have are earlier and not trustworthy on this problem.

Since the fan is a high current draw item, and especially after it ages, I was wondering if the points in the relay could be burned much like the contact points in a distributor.
The dist. points would be forcibly opened by the dist. lobes, but the relay can only rely on that weak little piece of spring steel after the trigger coil loses it magnetism.
I had an annoying problem (not fan related) on one of my old Harleys years ago similar this. At times the battery (6 volt) would be near dead in one hour after shutting the bike off. The problem was a sticking set of points in the voltage regulator that voltage ran through from the gen. to the batt.
The points were supposed to pop apart to prevent battery drain back through the regulator/generator. In this case, they were not popping apart.

If one can find the fan relay, and when the fan is running after shutting the engine off, one could try tapping firmly on the relay. If the fan quits running after tapping, (or whacking if the urge is strong enough!) this could verify the problem is the relay.
Maybe the owners manual, if available, would have the fuse/relay layout if the relay box cover is not marked?