So I have a 2003 s/crew with the 4.6, and what started happening is when I first start the truck in the morning, or on my commute home, it is building pressure in the cooling system, and will eventually overheat and I will have to pull over ( once bringing the engine up to temp) and I slowly open the radiator cap and relieve the pressure, once doing this the coolant seems to be sucked down into the system, and everything runs fine after that for my 70 mile drive home. Can someone please tell me they have seen this before??

 

Sounds like you need a new cap. Yea, they plug up. Throw some WD in there, blow it out with compressed air. Do this 2 or 3 times. If it doesn't work, get a new cap.

 

I actually replaced the cap already, I also replaced the thermostat... twice.

 

I'm curious if burping the system would help

 

Similar syptoms of a blown headgasketalso . I would have a block test done.

 

Yea, burping, or in other words, make sure it isn't holding air/ hot spots. Then perhaps a hydrocarbon test.

The 03 4six doesn't have an ECT does it? Yea, I think they were deleted in 01, - so, well can't burp thru there. They should have installed a valve for us in the heater core hose factory, sure would be easier bleeding these things out.