You can loosen the hose clamp for the upper radiator hose at the thermostat to let the air out of the system when it's running. I've used a screwdriver to gently pry the end of the hose to burp it. Or you could drill a small hole in the thermostat which helps the air escape when filling. My 4.0 had a temp sensor at the back of the head you could loosen up.