The escape or admission? If it is escape, it is easy for you to go on a ignition point or have the gas outlet obtained.
If it is admission, the heat can come from the cylinder head, if water circulates through the admission collector to heat the inlet air, (carburation and injection engines monophen, for example) you may have the croaded water steps stuck or that the butt joint is not exactly equal to the corresponding for that engine. If the water does not circulate well, the cylinder head is quite overheats, and if the water circulates erroneously by having poorly placed sleeves, the engine is heated and the collector as well.
Another thing that should be checked is the thermostat, seeing if it opens when the engine is heated is quite easy, you just have to put your hand in the hose that comes out of the thermostat to the radiator and wait for the engine to heat up, a point will come at which it first puts warm and almost immediately heating to the point of having to remove the hand of the hose, that means that the thermostat opens well.
If you do this same test playing the radiator panel you will find out if it is fine or if on the contrary it is half clogged. If it is half clogged, there will be cold areas and hot areas, if it is fine, the whole panel must be still hot.
All the best.