There's not a problem with them overheating. There's a problem with people letting the radiator screens (and radiator fins) get plugged with chaff, dirt, grass, etc. When the fins/screens get plugged, airflow decreases across the core, which then the engine gets hot. Once it gets hot, most people shut them down, let it cool, refill it with water, and start over. Wrong. The filler neck is plastic. It's really easy to deform if they're really overheated (which yours sounds like it was). Then the thermostat is usually damaged if it's original; and won't open properly, sometimes they open too soon, other times they don't open at all, and sometimes they are stuck open. There's a new part number for them but I can't say why it's a new number, they look the same. Maybe they changed the kind of wax that's used inside of 'em. Dunno.
Same thing for the BX series. Screen and radiator get plugged, people blame the "design" and cuss the little tractor, when there ain't anything wrong other than the person who's not doing the maintenance. See it all the time. "Well I clean that blankety-blank screen all the time".....yep...but never clean the radiator; and that's what's plugged. Screen's clean. Folks I ain't making this stuff up. Happens WAY too often. I really shouldn't care since I get paid to work on them. But at the same time, I want people to be pleased with their stuff-which means if I can help prevent big expensive repair bills and the associated dissatisfaction, I will try.
but for the short time I ran it, it started fine and didn't smoke... Im wondering now if I'll have to replace the radiator which looks expensive...