I am definitely losing some coolant from the radiator to the reservoir bottle. Does this mean that the radiator cap is defective and is releasing the press. in the radiator too early?

 

Each cycle from stone cold to normal will expand the volume of the coolant and send some to the overflow tank. It gets sucked back into the radiator when everything cools down. So unless you have to add coolant to the tank to keep it from going dry you're not losing anything. If you have any doubts, go ahead and put a new cap on - they can't cost much.

Most new cars have a better system than what is found in the EVO. Instead of an overflow tank, they have a pressurized expansion tank. The downside of the EVO type is that all the fittings have to be perfectly tight or else when the engine cools down instead of sucking back the coolant, the radiator sucks air. Then your overflow tank remains at the correct level but the radiator is low. I always like to check the actual radiator level occasionally, of course you need to let it cool down before you take of the cap.