Join Date: Nov 2016
Location: NE Ohio
Own a Commander?: Yes
Model year: 2006
Trim Package: Limited
Power-Train: 5.7L V-8 Hemi
If 4WD - system: QD-II
Current Mileage: 133,000
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?
I can't picture the 3.7 coolant reservoir. Does it have a cap? If so it could be bad an allowing pressure to escape and therefore allowing the coolant to boil over. The pressure in the system is partially responsible for allowing temps to exceed the boiling point of water without causing damage to the system.
Part of the reason you don't see bubbling when the cooling fan is running is because it's dropping the temp of the system below the point at which it is boiling. If you had a head gasket problem you'd see continuous bubbling no matter whether the fan is running or not; you'd also see your coolant level drop since the cylinder(s) that has the leak would draw coolant into the cylinder on the intake stroke.
Replace your radiator and coolant reservoir caps first - you may be able to fix the problem cheaply with just those two items.
2006 Limited, 5.7 Hemi, Tow Package, SuperChips tuner, Full Skids, RER MyGIG Upgrade. OME HD Springs w/ Bilstein 4600 shocks