I agree with Dave concerning a head gasket or cracked block causing an engine to run hot and it is possible for it to happen without the oil going to the crankcase. The thing that made me not suspect a head gasket or block is the fact that Jim indicated it was ok on a cool day. Generally the problem will exist at all temperatures if you have compression leaking into the cooling system. They make testers that check for carbon monoxide in cooling system. They go on the radiator cap. The ones I have seen have a blue liquid in them and as the engine heats up and the bubbles go through the tester the liquid will turn yellow if there is exhaust gas (carbon monoxide) present.