Anytime the cooling system pressurizes enough to push the spring back on the pressure cap, a little coolant will escape. Whether it ends up on the ground or in the recovery tank is your choice. If the recovery tank isn't there, air goes back into the radiator on cool-down and the level gets lower. With the tank, the coolant gets siphoned back in with vacuum.
Jerry

"It is better to be silent and be thought a fool than to speak and eliminate all doubt!" - Abraham Lincoln
Cringe and wail in fear, Eloi- - - - -we Morlocks are on the hunt!
There is nothing noble in being superior to your fellow man; true nobility is being superior to your former self. - Ernest Hemingway
Love your enemies and drive 'em nuts!