I have a 2.5 L v6 in a 97 ES. Almost every new trip, i have to take the coolant from the resivor and pour it back into the coolant cap. it always takes the whole resivor sometimes more. also while driving and at a stop light just idleing, when i start going again, you can hear the air and coolant bubbling through the heater core. i dont know whats causing this because according to the gauge, it isnt overheating

 

Bad radiator cap