Quote:

I want to differ with you on that. At any speed above 50-60km/h the thermo should never turn on, and you'll be reaping the benefits of not having a stock fan all the time. Wind speed under the bonnet won't be great enough to cancel out the negative effect the stock fan has through you're so called windmill effect, not nearly enough to make it as energy effecient as the thermo anyway.

Even though the thermo does sap power from the engine indirectly via the alternator when it does kick in, it'll mostly do so only when you're driving at slower speeds than what was mentioned, and never when the air moves through the radiator quickly enough to give enough cooling effect. It'll turn on very infrequently, and when it does it'll take much less time to cool the radiator to where it can switch of again. It'll do this because you can mount it flush with the radiator, and it'll be much more efficient moveing air through the radiator than what a stock fan could.

So probably 80-90 percent of the time you're turning a fan(which has enertia to overcome), trying to move air with it (which saps even more power because the blades act like paddles) and you're listening to that ugly whine of the stock fan. All of this when you don't need to.

Why then would most manufacturers eventually move over to either electrical or viscous(I hate these even more) fans? Because they save engine power which translates into better fuel consumption and better performance, because they don't use engine power when they don't have to.

Don't try to convince me that an A series engine with a stock fan will rev up just as quick as one without. 80-90 perent of the time it simply won't, and is probably the reason why guys shave of 2 of the stock blades sometimes...

I'm sure that even 80-90 percent is an understatement.