I recently replaced my fan switch and my radiator cap because the fan wasnt turning on which was making my car overheat. So i know my temp gauge works, the fan turns on now as well and the rad cap is not leaking or steaming. I drove the car for about 25 mins and when i got back home the resevoir was bubbling with boiling coolant. It was even leaking through the cap of the reservoir and made a nasty mess of coolant. The car was not overheating but i lost a good amount of coolant.

Is there air in the system? Also note that i did not overfill the reservoir when refilling the coolant (earlier today).

Thanks in advance.

 

could be the headgasket