Quote Originally Posted by UR LOSN View Post
I'd replace the cap. If it still continues...you "may" have a leak somehwere....not enough coolant is being moved through the system, and is letting in air.

does the fluid stay the same level in the radiator?
level seems pretty consistant, if not down a bit--but if the system isnt pressurizing properly, there will be more evaporation going on... so hard to judge.