I can't decide

I don't know how much and when to open the radiator. I've been adviced to open them to 100 on the runway, or in the air. I was also adviced that I should open to stage 2 while in the air so the engine is vented enough and the rest of the stages will not slow the plane down.

I open to 100 on the runway, I've never noticed a delay in speed. Now I'm confused because the radiator is said to slow down the plane. What should I do?

Alway's have the Rad open on 'Full Settings' are your engine will overheat and die m8. Depending in what aircraft you fly you don't lose much speed