I have an electric radiator fan with shroud. Is it helping at speeds over 55-60 mph or does it block air flow at that point? It's a pulling fan behind the radiator. Thx

 

Typically, the rule of thumb is fans are effective up to about 35mph. After that, air is flowing faster than a fan can pull. By 60mph, without wind tunnel testing, it's hard to say with 100% certainty how effective, or not, your fan would be. The guess would be; not much.

 

Fans don't block air flow significantly (running or not). One of my O/T modern car's manual said that the computer kills the fans as soon as vehicle speed hit 34 mph, as they are not needed, even with A/C on.

 

However, you darn sure need some kind of fan at idle or under 35 MPH.
Clutch fans allow the mechanically-driven fan to somewhat "get out of the way" when post-radiator airspeed begins to push on the fan instead of being pulled by it. As for an electric fan, it will pretty much freewheel when it is not powered. I don't think that you need to devise some sort of speed-sensing fan kill control unless you're running some seriously high compression fuel-sucking monster chupacabre under the hood. But, if you are, you can probably afford to have one designed and installed.
My 2c anyway..

 

Thanks, guys. I had a feeling that was the case, as the fan didn't seem to matter at higher speed. I have the fan on at lower and idle for sure, but I guess I'm using up electricity for nothing on the highway. Thanks again

 

I wouldn't worry about the electricity thing, personally. It's better to have the alternator work marginally harder than to risk overheating when you forget to turn it back on when you get off the highway and back in traffic.

 

If you are switching the fan on and off through the use of a temp sensor then there is nothing to be concerned about...the fan comes on only when needed.