i got a new overfill bottle from autozone today (universal) i was wondering how full it should be? there is no marking or anything on it, do i leave it full so that there is a constant flow into the line leading to the radiator or less than that high?

 

Less... hence the name over-fill. When your coolant temperature rises and then expands, it will need somewhere to go. I would leave it around 1/4 to a 1/3 way full.