M42 radiator wiring in early model former M20 car?

[jrdeamicis]

I'm so confused, I just went into the garage and pressed the a/c switch on my m20 that doesn't have any a/c or condensor fan anymore, and the engine still changes pitch like it is running differently. Clearly I don't understand the fan wiring and will shutup now.

The AC switch also sends a signal to the ECU to bump its idle to compensate for the AC compressor to be running. You don't need a fan or an AC compressor to make that happen.

[Jand3rson]

If you want to hook the electric fan to an OEM sensor you will need to run the wires. You'll need a different lower temp sensor for the radiator though. If it were me I'd just run a simple aftermarket fan controller.

http://www.summitracing.com/parts/FLX-31147/

Your local auto parts store will sell something similar too.

Forgive my ignorance here, but a different sensor than the one that's already mounted in the side of the radiator?

And if I'm going to be running a SPAL electric fan, you're saying you'd recommend going with aftermarket fan controller rather than the OEM sensor? Then what does that aftermarket controller wire into?

[328ijunkie]

Use the OEM fan wiring setup, it already has the relays and fan switch wiring in place. Use this 61-31-1-364-272-82 Fan switch and wire it to the high speed wiring (youll have to extend wiring to the pass side.). Then wire the SPAL into the high speed factory fan wiring.

This will allow you to set it up once and leave it and never have to worry about your cooling system messing up or you forgetting to turn a manual fan switch on.

[Jand3rson]

Awesome, the top sensor on the old radiator was the 364-272 part number, so I pulled it, cleaned it up and installed it in the M42 radiator. Now I just need to extend the wires over and hook that up, thanks to everyone for the info!

[bimmerteck]

Black/brown stripe wire and Green/black wire stripe connected to your fan switch should yield high speed, while Black wire and Green/black stripe wire will yield low speed, or connect all three to the 3 pin sensor and retain both speeds that the stock fan had.

[Jand3rson]

The 3-pin sensor that I pulled from the M42 radiator is 1 378 073, and says BMW 91°/99°C.

Do I want that one instead of the one from the M20 radiator? I would like to have both speeds, if possible.

[bimmerteck]

Yeah, for both speeds to work the three pin one is the one you want wired in. Snag an e36/e34 fan switch connector from the junkyard, extend the wires to the driver's side and I'll be like you never had an eta. :)

[AndrewBird]

The thermo switch won't give you two speeds though. All it does is turn on two different pins at two different temps. If you want multiple speeds, you need to have a resistor pack to give you two speeds. The stock AC fan has one on it. I doubt the SPAL you are getting does, but they might offer one.

You really don't need two speeds. I would just wire it up to turn on at the low temperature and call it good. You might even be able to get away with wiring it to the high temperature and then it won't turn on as often. We can also wire an override switch into the dash where ever so you can manually turn it on. This is nice if you need the extra cooling for whatever reason or if the temp sender decides to die while you are sitting in traffic.

[Jand3rson]

Then if that's the case, I'm just going to use the sensor with the 2 spade connections that I pulled from the old M20 radiator.

We'll wire a toggle switch into the dash with a label that says "FAN", and then have 3 others next to it that say "OIL SLICK", "MACHINE GUNS" and "SPIKES".

[bimmerteck]

The thermo switch won't give you two speeds though. All it does is turn on two different pins at two different temps. If you want multiple speeds, you need to have a resistor pack to give you two speeds. The stock AC fan has one on it. I doubt the SPAL you are getting does, but they might offer one.

You really don't need two speeds. I would just wire it up to turn on at the low temperature and call it good. You might even be able to get away with wiring it to the high temperature and then it won't turn on as often. We can also wire an override switch into the dash where ever so you can manually turn it on. This is nice if you need the extra cooling for whatever reason or if the temp sender decides to die while you are sitting in traffic.

True, the spal doesn't come with the resistor or the factory plug for the harness, but luckily BMW was nice enough to included one of each with the purchase of the car. Simply remove the harness/resistor from stock aux fan and connect to spal fan. Factory style control still gives you override via the AC button and makes for a very clean install.


Photo by systemdelete, on Flickr

[Jand3rson]

True, the spal doesn't come with the resistor or the factory plug for the harness, but luckily BMW was nice enough to included one of each with the purchase of the car. Simply remove the harness/resistor from stock aux fan and connect to spal fan. Factory style control still gives you override via the AC button and makes for a very clean install.

Don't have the stock aux fan, the condensor, or even the AC button. I ditched all of that a few years ago when I removed my entire AC system. I don't have any of the copper lines, refrigerant tank, or anything related to the AC anymore.

[bimmerteck]

Don't have the stock aux fan, the condensor, or even the AC button. I ditched all of that a few years ago when I removed my entire AC system. I don't have any of the copper lines, refrigerant tank, or anything related to the AC anymore.

Well that explains a lot, I was wondering why Andrew would want to do it any other way. :) In that case I would probably just run a single speed on the higher temp 2 pin sensor. I'm sure Andrew is capable of finding the AC wire behind the dash that overrides the low speed relay, wire a switch to it and leave the resistor out.(making the low speed of the stock harness the high speed now)

BTW- If using the toggle switch method be sure to put the fan on the "oil slick" switch and the oil slick on the "fan" switch. (keep 'em guessing)

[Jand3rson]

Well that explains a lot, I was wondering why Andrew would want to do it any other way. :) In that case I would probably just run a single speed on the higher temp 2 pin sensor. I'm sure Andrew is capable of finding the AC wire behind the dash that overrides the low speed relay, wire a switch to it and leave the resistor out.(making the low speed of the stock harness the high speed now)

Shit, he probably already knows which one it is. In fact, he's probably already got it figured out how and where he's going to run it.

[browntown]

Don't have the stock aux fan, the condensor, or even the AC button. I ditched all of that a few years ago when I removed my entire AC system. I don't have any of the copper lines, refrigerant tank, or anything related to the AC anymore.

So you ditched the recirc too? Don't you ever feel like you'd need it?

[328ijunkie]

dont reuse the 3 pole switch because the 91/99C sensor is too high. Itll turn on late and by that point the motor will be running quite warm :D.