Boost hasnt much to do with the radiator i am affraid. Boost is more like a turbo kind of thing. The higher you set it the more power your car gets:
- allows your engine to over rev
- uses more fuel
- damages the engine health
With the radiator you allow your engine to suck more or less air, which influences the temperature of your water and oil.
You can assign boost to certain buttons. Decrease & Increase, from 1-* . It's better that way in F1 as you can go from 1 boost to 6 or whatever without much problem depending on the situation in a race.