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Fitting twin electric fans by JST

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This is how I went about fitting a twin fan setup to my 1984 200tdi Defender 90, the principle will apply to any engine type or setup.

Why 2 fans Firstly they came available for a nice £10 and both fitted neatly behind the radiator and intercooler. By having two fans you also minimise the dead spot in the middle of the fan (where the blades meet) which tends to be bigger on a larger fan pulling the same displacement as two smaller ones.

With two fans you also have options one both together or running one at a time.

How they are switched The vehicle is used for long journeys to events, competing at low speed challenge events, playdays and for greenlaning including wading in various amounts of water and mud. I opted for a three way switch from Vehicle Wiring Products (not the cheapest but good quality). Approx £13 with bulbs, lens etc (sorry only photo that came out)


That way I could have:

Fans Off wading

One fan on controlled through a electronic thermostat to maintain correct coolant temp under normal conditions

Two Fans on needed when air flow is low with high engine speed eg bogged in upto axles (no air flow underneath vehicle) and high idle to keep charge in batteries whilst winching out.

Fan mounting, I used a simple configuration of angled steel using the sill at the bottom of the radiator (inside engine bay) with supports running upto the fan motors. Further support went from these to the two studs at the top of the rad housing. The wiring is cable tied to this angled steel. (will get a better pic from engine bay at some point)


I posted a thread on the wiring when I was fitting them as I ran into trouble and didnt have diodes. In the end I used the circuit diagram as below. The reason for not using diodes was I didnt have any, and wanted to make the circuit from easily replaceable parts that a typical garage would have lying around eg 12V relays.


All the +ve feeds to the switch are from an ignition controlled feed.

All the +ve feeds to the relays are straight from the battery with a 30A fuse fitted.

44/0.3mm 3mm2, 33 Amp wiring was used throughout.

For the electronic thermostat I did a fair amount of research. I was keen to have a system that would not compromise the integrity of the coolant connections. In the end I spent a fair whack £62.30 on a Pacet setup from Demon Tweeks (01978 6630009) they are expensive but where the only people I could find who sold it. You will need the 35mm Internal Diameter connections.


The Pacet box is multi adjustable enabling you to set the temp for the fan(s) to come on at and for how long you want the fan to run. Run time is set by how much you wish to reduce the coolant temp eg 5 deg, which is therefore determined by the efficiency/size of your fans. Both my fans are about 300mm Dia. Ideally you dont want to lower the temp too much (-10 deg for example) but you also dont want the fans cutting on/off all the time with +/- 1 deg. The box looks like this. The unit default sets to fans running if the thermostat in the plumbing fails (or you unplug it). You can just make out the two dials for the adjustment.


To determine the fan cut in temp I ran the vehicle upto operating temp and then let it sit on a high idle until the needle had just moved (at the top) past the vertical position (this took a good 5mins static running) (OEM coolant temp gauge) I then turned the temp adj until the fan cut in (a little red light also comes on the box to say the fan should come on!) I set the fan run time by trial and error so the fan ran until the gauge went back to the vertical. Approx 2-3mins for my fan setup. As the unit was soo expensive I also took the liberty of borrowing my wifes lunch box to mount the unit in. This is then cable tied up under the front wing behind the headlight. Out of interest my tdi coolant temp runs just to the left of vertical (a bit of black showing) under normal conditions. Static this goes upto vertical, 70mph for a while also soon gets the needle to the vertical position.


The internal switch is still to be mounted which will be done when I get around to sorting out the dash design I am going to go for. I appreciate that my veh electrics are a bit billy basic but they work for me and are not one of my stronger points. Yep point taken wires need tidying up as well.

So far all is well the only downside being my misses misses her lunch!

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