Solutions for dealing with when the fan should be on:
Always Off - Pro: Wireless installation, Con: You'll overheat.
Always On - Pro: Easy to install, just switch it to ignition, Con: You'll overcool the system and use energy when you don't need to.
Manually Switched - Pro: No special fan controller needed, Con: You'll need a way of knowing how hot your coolant is and you'll have to be very vigilant about turning the e-fan on at the right time.
Controlled using a specialized fan controller - Pro: It'll go on when it should be on and off when it should be off, Con: It's expensive.

 

Let's make a fair comparison, shall we? If the coolant is cool enough for the mechanical fan to be disengaged, the electric fan will be off... so the net losses will go to the mechanical fan.

As well, everyone is always simply discussing the drag put on an engine by a mechanical fan as it freewheels, or as it draws airflow, which does cost power, just as alternator drag does put parasitic losses on an engine. Converting mechanical energy into electrical energy and back into electrical energy does result in energy losses, thus the electrical fan, when turned on, should utilize more power than a mechanical fan of the same cooling capacity.

This makes perfect sense in a static system (constant rpm). However, when do we care about minor energy losses during constant rpm situations (cruise and idle)? The difference in fuel usage would be immeasurable.

However, the mechanical adds an additional loss to engine acceleration that the electric fan does not: increased rotational inertia, which is present whether the fan is engaged or disengaged. Everyone always talks about how much of a difference in acceleration a few lbs makes on the flywheel... the mechanical fan weighs a couple pounds as well.

I would bet that the mechanical fan's inertial losses would equal that of energy losses for an electric alternator. If anything, due to removing this inertial loss under all circumstances, this would add another advantage to the electric fan.

So you can all drop that energy conversion losses argument, too.

 

Remember that the mechanical fan is clutched to the eccentric...so it does not rotate at engine speed...

You need to measure the temperature of the coolant in order to decide when to switch on the fan, so the sensor must come in contact with either the rad or the coolant.

 

You Forgot a couple other things.

Stock fan freewheels when the air coming through the radiator is less than 150F. This means the engine is disconnected from the fan blades and is spinning on just the air flowing through it. Electric Fans typically do not move, resulting in a minor increase in drag and reduced air flow though the engine compartment.

And of course on a Electric Fan; the energy draw is typically increased/on when at freeway speeds because the coolant temp is up enough to trigger the fan on, however the stock fan is freewheeling (again disconnected from the engine). (This electric fan issue can be overcome with an additional relay that dis-engages the aftermarket electric fan when in 5th gear).

Most electric fans draw between 20-70 amps on start up, and around 20 amps in operation (although some of the Ford fans can draw up to 40 amps in operation). Using the 20 amp average (in operation electric fan) This translates to a .32 HP (SAE 94 standard) extra load on the alternator. Figuring that the average alt is only about 40% efficent (generous by most accounts as alternators are typically between 14 and 42% efficent when bearing and aerodynamic losses are figured in) that means that the 1 horse that you can get from removing the rotational mass of the stock fan is actually lost on load to the alternator.

If using that same formula, you have an alt that is at the low end (say an older S4 alt with 5+ years on it) and the efficency is really closer to 15 to 20%, there would actually be a net Loss of about 2 HP (SAE 94 standards again) in overall engine power (not even including the aerodynamic issues) when using an electrical fan over the stock fan.

But, we figure we are getting back 1 or two HP removing the mass of the stock fan, so that offsets the power draw of the electrical fan. So then the only load disadvantage of using a electrical fan is if the electrical system of the can can support it, as it would be a wash at 180F.

Of course you would still have the aero losses at freeway speeds (if applicable) for the electrical fan and of course unless the electric fan shuts off at freeway speeds (as mentioned above) you would actually be at a loss on highway power.

 

The post I made last night seems to have disappeared. Damn that's annoying...

Sure it'll work (i.e. turn the fan on and off), but the point is why would you want to let the engine get that hot?

Using the stock fan switch the fan will turn on at 97degC and turn off at 90degC.

The S4 fan temp switch is a Normally Closed switch that opens when it reaches the setpoint and closes when it drops below it. So disconnecting the switch mimics a high temp and switches the fan on. The S5 switch is the opposite.

That's good. I can't stress enough that the relay and fuse are not optional, and you must use wire rated for the current the fan will draw. Trying to got cheap here could easily result in an inoperative fan (and a cooked engine) or an electrical fire. If you're trying to do this in the cheap you should forget it and stick with the stock fan until you can afford to do it right.

Nothing I would use.

Then do it. Adjustable thermoswitches aren't expensive, especially compared to the potential costs caused by a bad set-up.

That worries me. Are you sure those fans will be sufficient? Because of its shape the FC's radiator is more effectively cooled by one large fan than two small ones. Another common cause of e-fan problems is poor fan selection...

This is true, my digital coolant temp gauge shows this very clearly. In steady-state conditions (idling or very slow traffic) the engine temp barely moves, unlike with an e-fan were it would be constantly rising and falling as the fan switched on and off. Not that this really matters much...

Not only is a proper e-fan install not as cheap as everyone thinks, but a replacement stock fan clutch can be had for about the same price as a decent aftermarket fan. The savings only come if you use second-hand OEM e-fans.

 

my step dad had an extra one off his camaro's and gave me the other one...