Not a trick, if the elec fan is a "slim_line" they may a std fan on the Crank,
Ask the owner?

I'm on non speaking terms with the owner. He's the master-dealer of 123 ignition.
When I was developing 1-2-Spark I had some good chat sessions with him about my ignition but nowadays he sees my as a threat/competitor..
Well I take that as a compliment

sorry very off-topic here...

if temperature-control of the motor is the issue I prefer the combination of a oilcooler with feed and return from the oilfilter-section with a thermostat in between : your engine warms up much faster, no over-cooling in winter and if you choose an oilcooler wich has a larger capacity than the original one the overheating risk is much lower - you keep the original fan & looks - everybody happy ....

In my "universe" the issue is, is that the fan fixed on the crankshaft uses 1 to 2 HP which isn't neccecary.. (all the time) for instance when your engine is warming up or cruising along on motorway and theres enough driving wind (don;t know the right word here) to cool the engine without using a fan.

Driving along 80km/h 12 hp is enough to run the car, (expering in my new old snail) without fan maybee 10 hp, this is almost 20% les power = 10% less fuel... that's what I'm after

Or more topspeed driving flat out (if the driving wind is enough to cool your engine down)

Mount the oil cooler in front of the fan...
http://www.cleanfix.org/products/cleanfix-vp_3

https://www.youtube.com/watch?v=q7btxXKqK6E

This was the surprising thing for me... Electric fan was ok around town, but out on a country road @ 80-100km/h this is when the engine would overheat, it seems obscure but it is a 2cv after all... This is where the design of the fan blades and housing was pointed out to me as such to force the air sideways and not through.
Like the yellow BMW 2cv, a better approach would be to have air flowing directly onto the heads, hence the cut outs in the wings, think that was an after thought because the electric fan was not enough in the first place?
For my purpose I want a fan I can stop to do through deep water on raids, instead of getting out to take it off, so a clutch type would be the best option, not on a thermostat but a simple switch.
As azuiper points out, if its more efficient cooling then a thermostat controlled oil cooler is the way forward, faster warm up and greater volume of oil and cooling area.

Harley

he might listen to you

problem with the 2cv is it uses Iron barrels which don't loose heat as efficiently as alloy finning in the BMW bikes or the visa which had a smaller oil cooler for its larger capacity.

When I have time! I will try to redo my clutch fan, the Belguim off readers also have a design.
Both designs use rhe clutch from an A/C pump
With a/c the pump will be off for much longer than its on.

When used on the 2cv it may be on much longer and the magnetic coil will/has got to hot and failed.
May try to use the clutch on its own with no coil magnet and a simple engage plunger?
Input welcome

Harley,
isn't an A series fan an axial/propellor type, rather than of radial type, which is the one that would direct the air 'sideways'?

http://www.engineeringtoolbox.com/fan-types-d_142.html

I'd guess that the problem with an electric fan was that above a certain forward speed of the vehicle, it's actually restricting the amount of air which can enter the ducting.

Try removing the metal or rubber cover behind the fan on a normal setup and see where the cooling air goes.
Years ago, I recall pulling into motorway services on the way to a 2CV event and found a 2CV in the car park which the owner said was suffering severe overheating.
Thinking it was the usual 'over-advanced timing' problem, I offered to check that for him, only to find that rubber mat missing.
Seems your guy wasn't the only one who hadn't done some basic research on fans...

All shown fans here are axial (including the electric fans). A Daf aircooled engine or Panhard have radial design, a radial design doesn't even look like a propeller... it looks more like a waterwheel!!!

Going on the findings Harley describes here, it may be that an electric fan gives more restriction then benifits at high speed.....



@sub-Pete, going on Hollyday in South-Africa the airco of the rented car was always on.
So shoulden't be a problem..