a thermostat sets the minimum temp it'll be, doesn't prevent it from getting as hot as it wants, and a 350 will easily get above 212, which is why they need a good system that can take a 14# cap, higher pressure allows higher temps .... if the temp is OK around town but climbs when you're idleing, the fan isn't pulling enough air thru the rad - if it gets hot at steady highway speeds the fan is most likely preventing enough air thru the rad then, need to check the fan cfm compared to what's needed with a 350
the milky oil is another side of the problem, but mostly the weather, it's simply a result of humidity condensing inside when the hot engine is shut down, only thing to do about it is avoid short trips, when it'll happen most, and change the oil more frequently .... you'll also get plugged pvc valves from that, which will make it worse
Bill
