Depending on how much the
oil pan is shrouded, the
oil temperature will usually follow the water temp. After all, the
oil flows in the block, not too far from the water. Under load, the oil temp will go up some. The oil flow is what dissipates the heat of friction from all the lubricated components.
It depends on your oil, but the maximum safe (running) oil temperature is in the 280F (~140C) range, and that's far from the oil's flash point. The thing to really watch out for is an unusual rise in oil temperature. It indicates bearing failure. Been there, seen that...