Radiator Fan Control System.

[MattDebbage]

When i bought my Excel earlier this year, the rad fans were simply wired to a toggle switch on the dash - manual control at its best
I tried to reinstate the original system using the otter switch - and discovered the likely reason it was bypassed in the first place - its a pretty rubbish design, unreliable and with very thin wire....
I looked into aftermarket switches, like the Pacet or Kenlowe, but to be honest I have used Kenlowe switches before and not had much luck getting them to seal. Also they would simply switch both fans on or off together, which seems a little crude.
I have therefore built my own fan switching system, based around a modern, reliable fan switch. It takes power directly from the starter motor cables, through double fuses, to a small (3" x 3" x 2") sealed relay and control box mounted low down on the inner wing, below the airbox. The standard wiring loom is not touched or cut in to in any way, and can be tied up out of the way. The original otter switch and pipe is replaced by a new, M22 threaded adapter, and a 3 pin fan switch fitted to this. Both fans are switched individually, and through seperate circuits so if one side fails, the other will still work. At 85 degrees (just over normal on the gauge) Fan 1 switches on, and if the temperature rises further, at 90 degrees Fan 2 comes on as well. As the car cools, Fan 2 switches off at 84 degrees, and Fan 1 at 79 degrees. In practise, this means that Fan 2 is very rarely needed, but will work to quickly bring the temperature down if for some reason one fan is not enough. The fans are not ignition controlled, so can cut in after engine switch off if needed.
I have also added an emergency bypass switch to the dash, a small square push button switch mounted under the cowling. Push this and both fans work regardless of engine temperature. This switch is ignition controlled, so it cant be left on by mistake.
Having used this system for the last 2 months, it has proved 100% reliable, and keeps the engine at a very stable temperature.
If anyone would like to copy this sytem for their own car, please PM me and I will supply a wiring diagram, photographs, and a parts list including where to get the parts from. Approx cost for you to get the parts would be around £50.
I am working on a similar system for single fan cars, that will allow variable control of the fan speed by switching through resistors to obtain the same result - i will post again when i have this up and running.
Matt.

[Lotus-e-Clan]

........In practise, this means that Fan 2 is very rarely needed, but will work to quickly bring the temperature down if for some reason one fan is not enough. The fans are not ignition controlled, so can cut in after engine switch off if needed...........

But that will only efficiently cool the radiator water of course. Without active water circulation the rad fan may stay on a bit too long on unusually hot days when the static water at the controlling fan switch (in the top hose) is kept at a higher temperature than usual, so battery needs to be good 'cos typically old school rad fans draw about 7 amps or so.

I found one fan is enough too, but I'm using an 80 L/min EWP instead of the std water pump which means the EWP and fan can work together with the ignition off to rapidly reduce the temperature and prevent heat soak. On the hottest of days (30+C) the water temperature in the cylinder head would reduce from 90C to 72C in less than 5 mins with the ignition off. Still need a good battery though 'cos it'll be drawing 14 amps (80 L/min EWP+fan) continuously over the 5 mins. However, in the normal British climate (up to 20C) the cylinder temp drops from 83c to 72c in less than a minute.

My full EWP system cost a lot more than 50 quid though but you could add a small pump to your system for peanuts and cover that eventuality. I use a small 1 amp 13 L/min slave EWP (cheap VW Audi) on the Clan which could be incorporated into your wiring for the fan control switch with the ignition off to actively circulate the water and rapidly reduce the temp throughout the engine instead of just in the rad...then you can walk away without worrying about the battery running down too 'cos Sods' Law states under bonnet heat soak could switch on the fan a minute after you have disappeared around the corner on a hot day! . 13 L/min is man enough with the engine off...you don't need full 80L/min in that situation.