Bit of a long post, but it might be of interest... I know this is a bit of a controversial topic, and I get why. The viscous fan when working correctly, is hard to beat.
Mine however, did not. Well it did - far too much. The fan is/was fully locked up I'd say 90-95% of the time, and resulting in a loss of power, MPG and the engine never got above 85-7c. Those of you that have seen/heard my car know it isn't that quiet. No centre silencer improves the V8 rumble no end, but its no fun when your viscous fan drowns it out entirely!
The ideal electric replacement fan would, by all accounts, be the 18" Lincoln Mk VIII fan found on various vehicles across the pond. Alledgedly rated at 4000CFM or so. Getting one over there is simple, getting it over here would be £200-250... err... no.
Looking at generic aftermarket options, Spal do a 16" 'HO' high output fan, that does about 3000CFM. I couldn't even find a price on that, so declared it unobtainium. All others I've looked at seem to top out around 2000CFM. And current draw on those topped out at about 10amps, which seemed a bit too good to be true.
A bit more googling looking at OEM fans pointed me at a pretty readily available Volvo 850/940/S70 fan... the internet suggests on low speed, its around 2500CFM, and on high its around 3300CFM. Best bit is, its about £30 on ebay, and another £15 for the Volvo relay module, which is a handy box that a) handles the current of the fan on high (about 30 amps running), and you just ground either the low or high speed selection to start the fan. A handy feature is high speed always takes priority - so if you hook low speed up to say, come on with air conditioning, and then have a thermostat for engine cooling on the high speed, the high always comes on regardless of what the low speed is doing.
It's a bit smaller than the mahoosive viscous fan, but not overly so:
I wanted a cowling/shroud that would get the fan pulling air across the whole radiator surface. Take one 600x600 network cabinet lid, and a bit of steel from one of the doors, and you're left with this:
And some fettling later. Sadly I didn't remember to take any pictures of the cowling with the fan in place, and the pegs on the bottom that fit into the standard radiator cowling mounts. The ears on the top are used to bolt the cowling to the radiator mount brackets - so the weight is hanging off the mounts holding the radiator, rather than the radiator itself. It isn't actually that heavy anyway.
Plenty of room!
The relay module can be wired up using 10mm spade crimps for the positive feed - the fan plugs straight in. The ground goes to the fan directly, again a 10mm spade fits nicely. The only problem is the speed selection that has round pins. I soldered some wires onto some red bullets, crimped them a bit smaller, pushed onto the pins in the module socket, and then filled with resin. Don't want them falling off!
Currently I don't have a thermostat - so I'm grounding the low speed before I set off and leaving it running. It's in the post...
Today it has been 17-18c all day, and I've had the fan running on low while driving around town, hooning it a bit, and letting it idle. At idle, it will keep the coolant temp down at 87c, with the A/C on too. Once I get the thermostat and can set the on/off points, it should cycle and keep the thing running proper temperature.
Best bit... I can hear my V8 again! And I no longer sound like a Nissan Navara pulling away...