Official Electric Fan wiring thread!

[Varinn]

I'm sure this has been answered in this thread, but I'll ask it anyways as a quick search did not turn up an answer to it. What is the average available space between a stock late model m20 radiator and the waterpump pulley on an S52? My oem aux fan appears to be dead and I'm considering replacing it with either a single 16" pusher fan or switching to a single 16" puller and removing the aux fan entirely. Will this be enough? Ambient temperatures in my area rarely ever exceed 30-35 degrees celsius and I do have AC in my car.

Lastly, I cannot quite figure out exactly what the best temperature would be for my fan switch, I'm definitely going to try and find a dual temperature setup. I know the m20 runs with an 80 degree thermostat from the factory, the s52 runs an 88 degree thermo. Will this make the stock e30 gauge read high when mounted in the head? An 82/88 switch seems too low for this setup, I'm thinking Something more like an 88/92 if available would be better?

EDIT: Found 91/99 degree was the factory aux fan switch for an S52, I may go ahead and just use one of those as I'm pretty sure the car will run cool enough that the low speed setting should keep temps down. If not I'll setup the switch to run on high at 91 degrees with an 88 degree thermostat

[fronton]

I don't have BK/BU from the original harness, I only have BK, GN/BK and Brown. Without the resistor involved when I connect GN/BK to spal RED and Brown to spal Black, the fan works on high. If I switch the spal RED to the BK it doesn't come on.

Does this mean that GN/BK is really still low but without a resistor it runs on high and my BK really is high but has a blown relay? I'm mostly confused because I don't have a Black/Blue.

When splicing the spal RED to high speed (whichever mine is), does that mean actually splicing it into the high speed line before it connects to the resistor or just double connecting it AT the resistor?

[RoadHazard]

BK/GN is connected to the low speed relay, which is turned on by the lower temp part of the rad switch. It's just a normal 12V feed so when you connect it to the fan directly, the fan blows at full speed. The resistor is used in this circuit to slow down the fan.

BK/BU is similar but it doesn't have any resistor, so the fan blows at full speed. It's connected to the high speed relay and turned on by the higher temp part of the fan switch. Your water has to get very hot in order for the high speed to turn on. That's probably the reason you didn't get power when you tested.

You could also check whether the black wire is actually the high speed feed by using a digital meter and checking for continuity between the end of that wire and one of the pins at the high speed relay socket in the fuse box.

[fronton]

BK/GN is connected to the low speed relay, which is turned on by the lower temp part of the rad switch. It's just a normal 12V feed so when you connect it to the fan directly, the fan blows at full speed. The resistor is used in this circuit to slow down the fan.

BK/BU is similar but it doesn't have any resistor, so the fan blows at full speed. It's connected to the high speed relay and turned on by the higher temp part of the fan switch. Your water has to get very hot in order for the high speed to turn on. That's probably the reason you didn't get power when you tested.

You could also check whether the black wire is actually the high speed feed by using a digital meter and checking for continuity between the end of that wire and one of the pins at the high speed relay socket in the fuse box.

Presently when I press AC it turn the fan on high speed, this was the only testing I was doing with the BK which wouldn't do it but the GN/BK does. Looking at the ETM diagram it appears that the AC control uses only normal speed which in my case is high speed because there is no resistance. I don't know why my BK isn't BK/BU but hopefully it is the same thing.

EDIT: BK indeed is what I have instead of BK/BU as my high speed, GN/BK being low speed. I connected BK and fan RED to the top end of the stock resister and GN/BK to the other end. The fan's BK is connected to the car's Brown for grounding. The resistor is mounted on one of the spal's motor screws. Low speed comes on at 10 o'clock but is able to keep it around 11 o'clock so I haven't been able to confirm high speed after a month. I'd rather be at the 1/2 mark when fully warmed but perhaps on a really hot day of hard driving I'll get there and be glad I'm only there. Thanks again for the help!

[RoadHazard]

That's exactly how it's supposed to work when you turn on the AC, i.e. power to the low speed and no power to the high speed. If that black wire is terminated at the fan plug then it's very likely to be the same as BK/BU because your BK/GN works exactly the way it's supposed to.

At this point, I would finish the loom first and see if everything is working or not. Run the car to temp and see if then fan turns on at both speeds. When the water temp needle points slightly before 12 o'clock, the fan is supposed to run at high speed.

[BlapBlap]

I did everything that was said by the OP besides putting in the 2 prong temp switch, but when I turn my key on, the fan turns on right away...any ideas why that would happen?

I have another E30 thats wired up the exact same way and I just use the A/C button to turn the fan on.

[mtlbloodshot]

I wish someone would post a step by step pictured DIY of this.

[AirplaneBuilder]

I used my stock AC fan and put some brackets together from bits of metal and mounted it up straight to my M42 radiator nice and solid and just plugged into the plug under the driver headlight so it all works fine now, i just need to push the snowflake button and bam my S50 cools. Its a redneck way to do it but it cost me nothing and super simple to do and if the fan ever fails there is unlimited amounts of used AC fans at junkyards for dirt cheap but since the stock fan has been working since 89 i assume they are pretty well built to last that long.

[bsturman92]

Ok EVERYBODY i need your help please!! I read through this whole thread and still having issues.... Please read this and tell me what you think,

So I have a 1991 318is wanted to do an electric fan swap from a Volvo. I got the fan. The only thing I did was cut the three wires at the aux fan and wire them directly to the Volvo fan.. It worked perfect and would keep me car cool for EVER. Except I would have to hit the a/c button to activate it... Wasn't a problem but my a/c doesn't work and at a stop while idling I would hit the switch and it would draw a lot of power m make my idle drop real low then go back up. (Just annoying as he'll) so finally I opted to buy a 3 prong switch from a e36ti which as we all know is rated lower temp.... So I unscrewed the old switch on the side of the radiator (big mess coolant drained out.. Good or bad? Car totally cold) and then installed the new switch and plugged my stock 3 prong plug right in....... Now the fan will not work what so ever no matter if I hit the switch or anything.. The fan works I hooked it up to battery... Someone please tell me what to do to figure this out.. I want it to work on its own... Very hot where I live and temp will slowly increase at stop lights ... Please help guys I'm going crazy

[Link]

Alright so I am still lost on this whole fan thing...

What I know... my fan has a Positive (Blue) wire and a negative (black) wire. I have a 3 wire plug behind my drivers head light with a brown (ground) and a Blue/Black and a Black/Green wire running to it.

What I think I know... The Blue/Black is a 12+ positive wire.

What I need to know... What is the Blue/Black wire, what is the Black/Green wire and where do I put the "Auxiliary Fan Switch 2-Prong" and what wire does it run inline with?

Thanks for any help!

[Link]

Alright so I am still lost on this whole fan thing...

What I know... my fan has a Positive (Blue) wire and a negative (black) wire. I have a 3 wire plug behind my drivers head light with a brown (ground) and a Blue/Black and a Black/Green wire running to it.

What I think I know... The Blue/Black is a 12+ positive wire.

What I need to know... What is the Blue/Black wire, what is the Black/Green wire and where do I put the "Auxiliary Fan Switch 2-Prong" and what wire does it run inline with?

Thanks for any help!

[Link]

Anyone got an answer to this^^^

[RoadHazard]

Link,

BK/GN is also a +12V wire. The difference is they are turned on at different water temperatures.

Go back one page and read post#148 and see if that makes any sense to you. Your fan's blue wire is the same as the red wire coming out of the fan in my diagram.

The fan switch, either 2-prong or 3-prong, goes to the radiator. You should already have a connector for it behind the RH head light. It's a black connector similar to the fan connector. See the diagram in the 1st post for wire colors.

[Link]

So under a great deal of reading on this I am this far:

On a 1991 318i behind the driver side headlight there is a plug.
Body side: Black/Blue, Black/Green, Brown
Fan Side: Brown, Black, Red

All of it runs to a resistor, then the red and brown wire go from that to the stock fan.
My SPAL fan has a Blue positive wire and a Black negative wire.

Can I just simply wire the Red to Blue and the Black to Brown?

If that works, then what needs to be done to the radiator plug on the passenger side of the car with a Brown/Black, Green/Black, and Black wire at it?

I don't see why I can not leave that as is and why I must use this part # 61-31-1-364-272-82, the two prong 80-88 switch.

Can someone help clarify some of this?

[RoadHazard]

Yes. Blue go to red on stock fan wiring. Black go to brown.

And no, you don't need to do anything to the radiator switch and its wiring if you already have everything.

The 80-88 degree switch will make the fan turn on sooner. But it being a 2-prong means that you can only run the fan at 1 speed. Stock is a 3-prong and when utilized with the fan resistor allows the fan to run 2 speeds. So, do you have to make changes to the radiator switch part? The answer depends on how you want your system to behave.