generally the thicker the wire the better. you need to find out how many amps the fan draws then look for a table like this to determine the guage needed.

just a normal 'open' relay will do (30/85/86/87 pins) and rated above the current you have determined you need

I think you might find unless the thermo fan is properly shrouded you might not get enough cooling from it.... unless are you going to run it with the original engine fan?

Don't understand that? run it with the original fan? :O

I'll see how it goes without a shroud. If it has problems, I'll make up a shroud.

My car seems to have some very slight, very intermittent overheating problem. Cruising at high revs temp gets up a bit. Thermostat is fine, Coolant level and condition is okay.

Gonna try a thermo fan to fix it

Let's say your current engine driven fan consumes 1Kw @ 3000rpm. (It might be a bit more than that, but let's stick to that for now)

For an electric fan to move as much air under same circumstances, it must also consume roughly 1Kw. That's 1000W, or roughly 83 amps at 12V.

Thermo's don't use anywhere near that much power - and that's a clue

Fatzook - I have no doubt you have no trouble with a digital controller and a 14" Spal fan.

That's a long way from a switch and a 12.5" unknown thermo though.

Steve.

Lump is correct I wan't talking about cooling efficiency - I was talking about power consumption.

IMO its 6 of one, half a dozen of another

Stock fans have nowhere near the efficiency of the blades as your better quality thermos, and that makes for very large air movement at reduced power consumption.

I love thermos, anytime I get a vehicle with an engine driven fan, 1st mod, before all others, is a thermo.

I couldnt find EFI, so I bought Throttle body off smileysmoke, but he kept both the throttle body and my money, so im stuck with carby, when Im dun building my toy, itll probbably get a coil pack baleeno donk.

I'm sure that people over think this issue.

A properly setup thermo that turns itself on and off doesn't actually use that much power. Assuming your radiator is in good condition, then half the time your thermo is off, there is no load on the engine from a fan, and the alternator is generating power as it usually does. Then the thermo kicks in, there is a small spike in current draw, then levels out and may draw 25A for about a minute ( if its not a completely shit fan, this should be enough time to cool the engine about 7-10degrees). Then it goes back to no load on the engine and alternator doing its thing.

A viscous fan works in a similar way.

An engine fan loads the crank all the time.

IMO its 6 of one, half a dozen of another