Run electric fans all the time?

DrCharles said
I don't agree that running fans are an obstruction. A fan that's stationary has more back pressure (to the air being forced through the grille) than one that is turning, since energy has to be expended to spin the fan and motor.

Not only that, the fan rating is at a specific back pressure on its output side (probably zero for pullers open to the engine compartment), and (AFAIK) assumes zero obstruction and atmospheric pressure on its inlet side. While driving at highway speed, the pressure of the ram air coming into the fan (after passing through the grille and radiator) is above atmospheric so if the fan's running it should move more air than its nominal rating.

However. It is true that there should be no need to run the fan at highway speeds. So why use a mechanical fan... which is turning all the time, even through a viscous fan clutch which consumes some power? :p

So either my t-stat is too restrictive (I just got a Milodon 16406 high-flow 180F to try) or my old copper-brass 26" rad isn't cutting it.

I started with a bare rolling shell, so I designed and built the entire wiring system from headlights to reverse lights. My 130 amp alt puts out 95 amps at idle. I can spare 40 amps to run the Contours when they're needed :) Not only that, the clearance to the core is so tight that even with the short Hayden fan clutch I don't feel comfortable running that big steel finger-remover.

The spinning blades create more drag, this is a fluid dynamics fact. They also create turbulence, which can slow the incoming air because of how it disrupts it. That last bit is specific to the particular radiator/fan/shroud arrangement, the speed of the blades, the volume and speed of incoming air vs outgoing etc... Which is why I say "at best" and "at worst". Unless you put it in a wind tunnel you can't know 100% for sure.

But given the efficiency to which modern cars are designed, you had better believe that if it was more efficient to run the fans all the time that's how modern cars would work. Especially since it would be a lot easier to just constantly run the fans than it is to program fan control parameters into the ECU.

Phreakish said
Not true. A windmilling fan blade will create FAR more drag than a stationary blade. The force created by the 'wind milling' is caused by lift created by the fan blades, and that lift creates drag. This is why propeller driven aircraft with controllable pitch propellers 'feather' the blades in the event of powerplant failure. In the radio controlled airplane world, motor controllers have built-in 'brakes' to stop the prop which helps reduce gliding drag too.

Yessir. And the fans on the contour motors do not windmill when the are not running.

@512Stroker, you can disagree if you want, but the simple fact is that if you choose an electric fan that moves enough air to cool your engine, supply that fan with enough power to run as it's designed and control the run time of the fan accurately the electric fan will work better and steal less horsepower from your engine. That's the engineering that makes it work on new cars, it's no different for a retro-fit. If you pay attention and build an appropriate system for an aftermarket upgrade on one of these cars it will work just as well. It's no different than picking a carburetor and building a fuel system to supply a higher horsepower engine. If you run an undersized carb and starve it for fuel, you get a poor result. You wouldn't say all carburetors are bad in that case, you'd just get a bigger one and supply it better. Same deal with an electric fan. People fail with their electric fan retro-fits because they either don't pick fans that move enough air, they don't wire them appropriately, or they don't control them accurately. Or some combination of all of those factors.