[old_master]

From what you have posted here, it appears that you have no leaks, either internal or external. Let me attempt to clarify your confusion. Increasing engine temperature is what causes coolant pressure to increase.

The fact that you just purchased this vehicle leaves a lot to the unknown. You have no idea of the history of this vehicle. Perhaps the last owner sold it because of this problem. Maybe because the last person that worked on it was just a mechanic, not a technician. Maybe the intake gaskets were leaking oil and after installing the incorrect gaskets, the engine started overheating and he gave up. Who knows? If the incorrect gaskets were installed, this would create a restriction in the flow of coolant through the entire cooling system therefore causing the overheating. The passages in the cylinder heads and intake manifold are part of the main coolant flow. The fact that the radiator is cool and the engine is hot confirms this theory of restricted flow, (provided the thermostat is working correctly). The only way to know for certain is to remove the intake manifold, carefully remove the gaskets and take them to a GOOD auto parts store and compare them to the proper ones. Pay close attention to the positioning and diameter of the coolant passages in both sets of gaskets. Before reassembling, make sure the coolant passages in the heads and intake are clear. This scenario most closely fits your set of symptoms, restricted coolant flow through the engine. Like mentioned earlier, you don’t know the history, therefore you have got to start with the basics. RULE OF THUMB: Always keep in mind that the guy that worked it before you didn’t know what he was doing.