2004 ford explorer

sounds like a compression leak into the cooling system. plugged radiator is another possibility but shouldn't have started all of a sudden. you need to pressurise the cooling system and check for leakdown. no leakdown ? check the radiator.

I've checked multiple vehicles in my day the old fashion way, by pulling the rad cap to see if it smells like gas, and check the oil dipstick for a white creamy texture. but to me it sounds like u may need to change the thermostat if u haven't already, also the temp gauge sensor. good luck I own a 1995 v6 4x4 with 150k, its a very reliable smooth running vehicle for its age