Radiator question

The people that suggested using a non-contact thermometer I think are correct. You should use it too also check the water temp coming out of the engine and see if it is close to the opening temp of the thermostat. It may reach a few degrees (up to 10 or so) until it opens and the temp levels out. As the others stated-you should have about 20-30 degrees drop across the radiator. I believe the engine block is OK. I think it will be found as a faulty thermostat or the fins loose from the core of the coils.