Cooling Issue
 

'94 with the 3.0. New water pump, new t stat, new radiator, new radiator cap, etc. Used funnel to burp it and did that 3 times. Also did the blue liquid head gasket test and it checked out good and had a person do a pressure test and he said it checked out good. It gets up to temp and we got the t stat to open up the last time we burped it (not sure it opened the time before that). Drove it about 15 miles with speeds from about 35 to about 60 and it held the same temp the entire time. Got home and when I shut it off it boiled over into the overflow. It has been doing that since we got the new water pump. Never had it boil over before we did the water pump and some of these other parts. The people we got it from said it overheated on them once and when we got it the overflow bottle was melted a little on the plastic cap and the radiator neck appeared melted so we replaced them with a stainless overflow bottle and new hoses to that and parts because we figured probably a bad radiator cap. Any ideas why it would boil over like that still? A mechanic I know had it for a couple of days and when he ran it he got the same thing where it would idle for a couple of hours just fine and then when you drive it the temp seems fine and when you stop it boils like that. He thinks head gasket but I'm not totally sure with the fact pressure test was good and the exhaust gas test was also good. Temp reads almost right at 1/2 on the gauge once it warms up the entire time. New radiator cap also doesn't feel like it fits as tight as the old one and we tried another new radiator cap also and it fit the same. Any ideas here?

Did a pressure test myself and found a couple really small leaks on heater hoses and one on lower radiator hose. Fixed those and ran it again after burping it and same issue. Any ideas?

Hows the fan clutch?
Also, since it has been overheated that you know of atleast the one time and things were melted, might want to try a leak down test