Does the motor diesel at all? What kind of carburetor do you have? My junker Rochester B would ALWAYS percolate and the floats would stick... I've gotten use to carrying around a long screw driver so I can whack it a few times; should it decide to throw a fit.
It seems to work, the floats unstick that way. If you have a Rochester B, consider getting a Monojet! Check timing, valves, blah blah blah.
They've got special chemicals (kind of like liquid Drain-o) that you can flush through your cooling system and then replace all of the water 2 or 3 times. I know a 250 isn't a 216, but I think that 180 deg is perfecly acceptable. My engine runs reall good up until 200deg and then begins to crap out on me. So I figure anything between 160 and 190 is acceptable, after that is when I get paranoid.
So, you should go to a 160 thermostat and just flush your cooling pipes.
