Hi All. I am pretty sure I have a head gasket leak - this one in my 3.7. What I'm wondering is why I am seeing bubbling in the coolant reservoir on a certain cyclical pattern. When the aux fan is running there are no bubbles. As soon as the fan stops running I get a good stream (all of this only when I have the pressure relief valve open on the rad cap). Any ideas on why it's happening that way? Is it because the thermostat is open when the fan is on and it only forces the air out once it closes?