There are three reasons why you would want to fit an electric fan. Firstly, the belt-driven fan absorbs a considerable proportion of the SJ engine's puny power output that would be better used getting you out of the mud. Secondly, the engine warms up more quickly, reducing wear. Thirdly you can switch the fan off before entering deep water. This is how I fitted one to my car.
I removed the fan belt, fan and spacer, then refitted the pulley with shorter bolts. I removed the fan cowling and fitted two brackets horizontally across the back of the radiator, using the captive nuts that held the fan cowling. I made the brackets with 25x25mm right-angle steel section bought from B&Q, with a piece of steel welded on in the middle to give them extra depth.
Next I got an electric fan. The best place for these is a breaker's yard, and you want to look for an older car because the newer ones tend to make the fan an integral part of the front grille. Mine came from the hydraulic oil cooler on a lorry, and it was exactly the right size to fit between my brackets. You can put the fan in front of the radiator if you want, but I think my method is the neatest. Make sure the direction of airflow is correct; if not you need to reverse the fan blades as well as the wires.
A thermostat is needed to control the fan. I bought mine from www.farnell.co.uk, part number 560-250. The thermostat is fitted in a plastic box bolted to the radiator support bracket, using rubber grommets to protect it from vibration. The thermostat bulb fits nicely into the channel that runs around the radiator header tank, under the top hose connection, and is held in place with the black springy part of a bulldog clip.
The circuit diagram below shows how the fan is wired up. The fan draws over 10amps on startup, dropping to 4amps when running, so a relay is essential and the supply should be fused. I used a heated rear window switch from a scrapyard SJ; this has a bulb that lights up when the fan comes on. The switch is normally on, but can be used to turn off the fan when approaching deep water.
I adjusted the thermostat so that the fan comes on as the temperature gauge approaches HOT. In practice, the engine thermostat keeps the water temperature at NORMAL for most of the time; it's only on the hottest days in slow traffic that the fan cuts in.
UPDATE! Having run this installation for the best part of a year, I have identified a problem with the thermostat bulb mounting. It's OK off road and round town, but when travelling on faster roads the air flow over the radiator cools the sensor down so much that the fan will never come on, and the temperature rises too high. I haven't done anything about this yet, but I plan to fit some microbore pipe insulation over the sensor to reduce the cooling effect. If that doesn't do the trick I will probably put the sensor inside the header tank, as is done on the Kenlowe installations.
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