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Discussion Starter · #1 ·
Ok, here goes. I have a 1997 318i with M44 4 cylinder engine. The radiator fan doesn't run on low speed and causes the car to overheat. Using the Bentley Manual, I have not been able to pin point the root cause. Thanks.

I have done the below:

1. Jumped the black/green and brown wires at the Fan Temp Switch with Ignition On. Fan doesn't run
2. Jumped the black/grray and brown wire at the Fan Temp Switch with Ignition On. Fan runs on High.
3. Checked both #16 and #48 fuses.
4. Removed the low speed relay and have power at terminals 6 and terminal 4 of the low speed relay socket with Ignition On.
5. Replaced the low speed relay.
6. Checked continuity of all wires from Fan Temp Switch to dme/relays.
7. Ran 12 volts to fan via terminal 2 of low speed relay socket and fan ran fine.
8. Checked low speed relay socket terminal 5 and only getting approximately 5.8 volts. Then jumped wires in step 1 above and voltage didn't increase.
 

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D'oh, You Kids!
1984 633CSi, 1985 635CSi, 1985 325e, 1987 325is, 1993 325is, 1995 318is, 1995 M3, 2003 F150
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If the mechanical fan and clutch are working as they should, the system shouldn't need the help of the electric fan unless you are running the AC wide open continuously and you're in an area with extremely hot weather.

With that said, your low speed windings on the electric fan are kaput according to your pretty thorough testing.
 

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D'oh, You Kids!
1984 633CSi, 1985 635CSi, 1985 325e, 1987 325is, 1993 325is, 1995 318is, 1995 M3, 2003 F150
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31,082 Posts
That's why it's overheating. No mechanical fan= much greater risk of overheating. I know, I know, lots of people have done the fan delete mod and have had no trouble....yet., but I'll ask you, why, on a car that is so sensitive to overheating, would you risk overheating it by deleting the primary method of cooling the engine? I know YOU didn't delete the mechanical fan/clutch, but someone did.
 

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Agreed but still need to determine why the electrical fan doesn't run on low speed
Ken, gave you a possible answer in his earlier post. There are two sets of windings in the fan motor, one for low speed, and one for high speed, with a common ground connection. If one of the windings is open, the fan won't run at that speed. If you have an ohmmeter, you can check the resistance of each of the windings to verify whether or not the low speed winding is open.
 

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Discussion Starter · #9 ·
The low speed was 1.3 ohms and the high speed was 0.6 ohms. Also, when jumping the low speed at the radiator temp switch, there is no voltage at the fan connector. But when jumping the high speed, there is battery voltage at the fan connector.
 
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