Coolant in my 2003 F250 Diesel 6.0 is boiling out degas bottle. Can hear coolant "boiling down" after I let off gas pedal, then get steam from under hood. Does not do this every time I drive it. Just had egr delete and oiler cooler, radiator, hose, reservoir and thermostat replaced. Temp gauges seem to work, never show high temps. No white or black smoke anywhere. Heater in cab works fine. Engine performance seems to work great. Am working on getting the right tester to do driving coolant system pressure test. Is this LIKELY to be a head gasket problem or does it sound like something else...if so, what do you think it could be?!? Help!

 

It could be head gaskets or it could be just the cap itself, do the pressure test and if the pressure is popping before 16lbs then you know it is the cap, also make sure you are not overfilling the resivoir, it should only be filled to the MIN line, the MIN line is the new max line as FORD added a new label to alot of trucks after realizing what the coolant level should be.