Fitting Electric Fan

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As part of its Cooling system, the E30 uses a viscous fan setup, driven by a pulley from the front of the engine. While efficient, this arrangement takes up a lot of space; too much space if you've undertaken an engine swap to a larger lump. If you've sacrificed those precious inches to a bigger engine, here's how to replace your fan with an electric alternative.

Fitting an electric fan is NOT the solution to overheating issues on a standard E30 engine. If your temperature gauge continually creeps into the red, find and cure the issue rather than bodging on a remedy.


Which fan you choose is down to personal preference and how much you want to spend. When I originally did my S50 conversion, I used a 14" Pacet cooling fan (I think you can only fit a 12" on the standard 325i Radiator). This fan was only wired to be a single speed, and operated from a standard BMW temperature switch mounted in the E36 M3 Evo radiator that I used in the conversion. This radiator already had the mounting hole for the sensor, so it was easy.

As part of the A/C install I'm currently doing, I have removed the Pacet fan, and fitted an E30 M3 cooling fan which is mounted as intended on the front of the A/C condenser rad. The E30 (M3 or otherwise) A/C fan is the same fan as used on the M3 that does not have A/C. BMW can supply the correct brackets to mount this fan without mods or drilling extra holes.

Non-BMW fans have also been fitted. To fit one (in this case an RS Turbo fan) I made up some small 'L' brackets that bolted to the side of the cooling fan, and then mounted this directly to the front of the radiator using the Pacet 'quick mounts'. These are a bit like round zip ties. You poke them through the brackets on the fan, through the radiator fins, and then push a fixing plate on the engine side of the bit that pokes through the radiator. These are quick, easy and require no extra holes in the car.

Temp Sensor

You first need to decide what temp sensor you are going to use. Obviously, the neatest option is to mount a BMW sensor in the side of the radiator. Unfortunately, not many standard E30 radiators have the hole for this. If you're lucky (or have a non-genuine radiator), you may have a blanking plug that can be removed, and a BMW sensor fitted in its place. If you look at the side of an E30 radiator you can see the moulded boss where the mounting hole would be. It may be possible to drill and tap a suitable hole (M14x1.5).

If you can't use the BMW switch mounted in the radiator, then you are going to need some sort of adaptor that mounts in the top or bottom radiator hose. The adjustable one mentioned above is nice, but rather expensive. You can also get an adaptor that just has a threaded hole in the side that will take any temp sensor you have (various threads available). Another possible option, is to modify the metal cooling pipe that runs across the front of the M20 engine. If you got one of these, and had a suitable mounting boss (M14x1.5 nut) welded to it, you could use a BMW sensor.

The temp sensor cannot be mounted in the thermostat housing. This is because the temperature at this point is the running temp of the engine, determined by the water thermostat, and should remain constant. If you placed the sensor here, it would either not switch on until the engine is already overheating, or, because of hysterisis in the sensor, wouldn't switch off again.

The purpose of the coolant in the radiator is as a dump for excess energy in the engine coolant, as determined by the thermostat, and must always be cooler than the water thermostat's operating temp.

The part number for the 80/88 degree switch that I used is 61 31 8 361 787.


The wiring I use is just a copy of part of the BMW auxiliary fan wiring. You just use half of the circuit for a single speed fan, or all of it for a double speed. In most cases, a single speed is all that's required. I have only changed mine to dual speed as I need it for the A/C operation. The E30 fuse box already has the correct spaces for the fuses and relays that need to be fitted. You just need to get the correct crimp terminals for the fuse box.


You have three choices for fuse crimps (depending on the size of wire you are crimping).

Size No. BMW Part
small wire 30-851 61 13 1 370 691
medium wire 30-852 61 13 1 370 692
big fat wire 30-853 61 13 1 370 693
Relay Crimps
small/medium FBL6
medium/large wire FBL66
wiring connector 61 13 1 378 410
contacts 61 13 0 007 441

The relay crimps can probably be found at the dealer, but I can't easily find the correct part in the ETK. These crimps are actually nothing special, and can probably be found at Halfords etc. They are just regular (non insulated) female spade style crimps, but they must have the little latch to hold them in place.

The plastic wiring connector plugs into the radiator temp switch, and the electrical contacts that are used with it. You will need two of these (or three if you want to go for a two-speed fan)

Fuse Box

The fuse box already has the correct 12v feeds etc, so you don't need to find power. There are two fuses needed for a single speed fan (18 & 19), and three fuses for a dual speed (3, 18 & 19). You will find that one side of the fuse already has an internal connection. You just need to add the wires that run from the outer end of each fuse.


Power leaves the fuse box via fuse F19 and goes to the input side of the temp switch. The output side of the temp switch then returns (one wire for single speed - two wires for dual speed) to the fusebox and goes to the fan relays. Relay K1 is the low speed relay, and K6 is the high speed. The return wires go to relay terminal 86 (If you are wiring a single speed fan, you only need to use K6). Pin 85 of the relays needs to be connected to GND. You can just run a wire to any suitable GND point.

Once the wiring is installed as above, you will find that when the temp switch closes, you will get 12v leaving the fuse box (via F19), and returning to the relay which will close. If you have wired both the low and high speed, then the relays will switch at different temperatures. Initially the low speed, and then the high.

You now need to wire the output side of the relay to the fan. The high speed is on F18, and the low speed is F3. Just run a wire from these fuses down to the fan +ve wire. If you are going for a dual speed fan, you will need a low speed fan resistor to give the slower speed. This should already be present if you are using an E30 A/C or M3 electric fan.

What you basically end up with is both the high and low speed wires connecting to the same +ve fan wire. It's just that the low speed wire needs to pass through the resistor before it connects to the fan. The -ve side of the fan just connects to a suitable GND point. There's a good one just behind the passengers side headlamp assy.



Your E30 has some of the wiring in place in the fuse box to automate the fan. The diagram above is if you want to add to the OEM wiring. The bits/wiring you will need to add are arrowed. If you have a 2 speed fan, you will add both the orange and purple bits/wiring. You will need to add the female spade terminals into the fuse box for the relays K1, K6 and the fuses 3, 18, 19 and the wiring to the fan/temp sensor.

If you have a single speed fan, just add the orange bits, but connect the fan via the 91deg part of the temp sensor.

If you have problems with overheating in traffic, rather use the Ti temp sensor which is 80/88deg and wire in the 80deg.

Hopefully that makes some sort of sense.

Written by ian332isport