Radiator cap boiling over
I got to work today and got out of my truck
and I heard something sizzling under the
hood. I popped the hood and Coolent was
boiling out of the Coolent reservoir with the
cap still on it. I also noticed that the
reservoir was swelling up and as the motor
cooled the swelling went back down and
Coolent went back into the motor. Any
ideas what's wrong?