I have owned my MGB for over 47 years. I mention this because over time it has become more of a challenge to keep the car on the road. We have seen the introduction of unleaded petrol, the closure of the MG factory and dealerships leading to poor repro parts, and the recent blanket 20mph urban speed limits (which my car hates).
Around six years ago I started considering the fitting of a modern electric cooling fan to the B. Looking at what was on the market, there seemed to be offerings from two main suppliers, both
well made, but requiring a lot of ‘meccano’ to mount the fan unit and intrusive sensor system. They are also quite expensive. This started me looking at an alternative solution; after all it’s only a fan and a simple way to control the temperature.
Initially, I only wanted to fit a fan and control this manually with a dash mounted switch. So I made up a shopping list. After measuring the radiator and looking at available fans, I found a nine-inch complete with fitting kit for around £20 on the internet with the ideal dimensions to
mount directly to the radiator core. Next was a relay, switch, wire and connectors. I purchased these from one of the specialist car electrical suppliers. Total cost including the fan was around £35.

My car is a 1974 car, so negative earth, centre console and fitted with the same front loom as the GT. However, the following can easily be adapted to fit positive or negative earth cars. I have tried to make no reference to polarity, as MGBs are both positive and negative earth.

FITTING THE NEW FAN:

To fit the fan, you first need to remove the mechanical fan mounted on the water pump. Slacken the fan belt, knock back the tab washers, and remove the four bolts securing the fan to the water pump pulley.
Remove the fan and replace the bolts, tap the tab back over, and retighten the fan belt.

Start by fitting a two-way connector block to the new electric fan wires. (This makes any future maintenance easier.) These type of fans can be reversed to either pull or push air through the radiator. Before fitting to the radiator please ensure the air is flowing in the correct direction.

Then locate the fan on the right-hand engine side of the radiator, between the top and bottom header tanks, ensuring it clears the water pump pulley. The fan comes with what I would describe as linear cable ties.

They have a pad on one end, and notches on the shank where a second pad can be pushed on, securing the fan in position. Carefully pass the ties (fixed pad engine side) through the fan and radiator fins, then push on the separate pad until it loosely secures the fan. Fit the other three ties, then tighten all the ties to secure the fan to the radiator. Cut off the excess.

WIRING:

Start by mounting the relay to the inner wing close to the existing wiring loom. (I used an existing fixing mounted in the wing.)

The relay has four connections (85, 86,87 and 30/31). Pins 87 and 30/31 are the heavy duty contacts. Pins 85 and 86 are the energising coil connectors.

Fit two wires to the other part of the two-way connector, and plug the two halves together to the fan. Run the two wires from the connector along the radiator diaphragm. Fit a ring connector to one of the fan wires (check polarity to give correct rotational fan direction), and connect it to earth using one of the radiator diaphragm mount bolts. Take the other wire and run along the existing wiring loom to the relay pin 87. Then connect a wire from pin 30/31 of the relay to the fuse box. Mount the switch into the dashboard. (I mounted mine in one of the round holes in the centre console.) The switch I used has a built-in LED to show when the switch is active.

NOTE: THIS IS POLARITY SENSITIVE:
Care should be taken when connecting it up, depending on the polarity of your car.

Negative earth cars: Connect pin 86 to ground and the wire from the switch to pin 85.

Positive earth cars: Link relay pins 86 and 30/31 and connect the wire from the switch to pin 85.

Note: The gold pin on the switch must be connected to negative 12 Volts.
My car is fitted with the same front loom as the GT, so I was able to use the Green and Black/white wires located behind the centre console, normally used for the heated rear screen, to connect the switch to the relay. The Black/white wire from the HRS re-appears in the bunch of bullet connectors below the fuse box, so saves feeding a separate wire through the bulkhead. I used this to connect to the relay.

Operation:

Once all connected up, checked the operation of the fan by operating the switch and checking the LED indicator light comes on when the switch was operated. Initially the LED was on all the time but changing over the Green and Black/white wires resolved this.

In operation, what really surprised me was how infrequently I needed to operate the fan. It was only when stuck at traffic lights or in long queues for any length of time that I needed to use the fan.

My car is fitted with a dual gauge, with the temperature section being divided up into C – N – H. Under normal operating conditions, the gauge sits at the seven o’clock position. I would wait until the gauge reached the six o’clock position before needing to operate the fan.

Mike Barclay