HELP! 92 Explorer overheating

[J_Birk]

My 92 Explorer is overheating after running 15-20 minutes. The temp gauge goes up to the L or higher and it the engine is killed, it boils water and coolant out of the overflow container. I have replaced the thermostat twice, had the radiator completely boiled out and all leaks fixed, replaced the fan, clutch and water pump. I am a mechanic and this has me stumped! No water in the oil or coming out the exhaust I am thinking a blown head gasket, but would appreciate any advice before I tear into the motor.

 

[Commtech]

My wife's 95 Windstar had a problem overheating and we did not catch it until too late (major boil-over on the road). Seams the rear side of engine was clogged and not getting enough coolant. Warped heads and messed up valve guides by that point. Cost us major bucks to get fixed.