Fitting a thermostatically controlled fan switch - by Michael beswick

Since fitting the supercharger, the car runs a bit hotter when caught in traffic. Whilst not actually overheating, the gauge reads quite a bit higher. I was also concerned that the original 3 blade metal fan might be tired. There have been a few reports of blades shearing and coming up for air through the bonnet!

Consequently I wanted to fit a 7 blade plastic fan. This might be more effective -only time and the summer will tell. I already had an electric fan, controlled by an "Otter" switch. (When it gets 'otter you turn the fan on....), so I thought I would fit a thermostatic control.

Getting the radiator out should take 20 minutes; it took 2 hours! With the s/c belt and associated pulleys, there is insufficient room to pull the bottom hose off the water pump. Eventually by sliding a (large) screwdriver between the pipe and the water pump I levered it off!  Of course, to get at the fan, the radiator removal is necessary unlike the later r/b cars with the standard electric fan and radiator mounted further forward.

I had the radiator pressure checked as I had been pulling and pushing the connections.....The thermo switch was supplied by Car Builder Solutions.  They can also supply the top hose fitting with M10 thread to take a thermostat sender, but in this instance it was felt that the fitting of of this in the top hose on a B might cause some stress, hence the use of the union.

The thermostat sender was similar to the Kenlowe but cheaper. It also had the probe that looks as though it comes out of a domestic fridge, but a threaded union was also supplied. The probe can be fitted in the top hose but I've always felt it looked rather Heath Robinson, and was a leak waiting to happen. The radiator firm fitted the union in the top tank and fitted a drain plug in the bottom tank, as I intended to use 4Life coolant fluid.

The control was fitted beside the secondary fuse box. The suggested wiring was to run a supply to the control, and from that to the fan. I already had a relay in place with the original "otter" switch, so I wired the thermo-switch to trigger the primary relay circuit. The warning light light also comes on both when the thermo-switch kicks in and also the "otter" switch. The current required to trigger a relay is tiny so I used a 1A fuse. (The fan circuit is also fused at 15A)

Originally I fed the relay circuit from an un-switched supply (terminal 7 on the fuse box). This would have meant the fan continuing to run after the ignition was switched off (as the radiator temperature would rise). Although unlikely, it could place a long drain on the battery. Also it would cool the radiator but not the block. Starting the engine would then dump a volume of cold water into the block. Under the original mechanical system, when the engine was turned off, everything stopped. Engine, radiator and bonnet quietly cooked...but it seemed to work! So I subsequently wired it to a switched terminal (5) on the original box.  Of course, one could always upgrade to an electric water pump and allow the water to circulate for a period ensuring the unit switched off after a pre-set time.  No doubt those with the electrical skills could come up with a solution.

I think it's a worthwhile modification, but only if you have to remove the radiator, and have a local radiator builder. Or you are good at brazing.........

Michael Beswick.

Below, the thermostat fitted through the mounting boss in the header tank.

Below the relay and thermostat control.

Compare the neat and tidy approach above to that on Phil's car below - time for an update!  The one below was part of the original installation by Frontline and just one of those jobs not yet sorted!  Note also the additional foam added subsequently and is an original part but often missing, as is the rubber strip on the top of the radiator diaphragm.

And below is my 11" Pacet fitted on my 1980 BGT:

This is a simple installation on a later rubber bumper car as I simply wired it into the existing thermostat switch at the top of the radiator.  The wiring was later properly clipped out of the way.  Make sure that when wiring it up it blows the correct way and sucks air through the radiator and doesn't try to push it forward through the rad.  One of the planned jobs is to recondition the radiator and fit a proper thermostat switch as Michael has done above, and put the fan on a relay instead.

The worst part of the job is pushing the ties through the fins, but so far the unit has held and no sign of damage.  The arrows indicate the cable tie pull ups.

The picture below shows a modified Revotec sensor as fitted by Stuart Longstaff.

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