as gsxr calls it: "high cold pressure" symptom, this is a test for the curse of the aluminum head crack syndrome.
A minute crack in the casting allows combustion gas to enter the coolant system and this pressure stays there overnight (unless the head gasket or a hose is leaking).
The test is simple: In the morning, with a cold engine, pinch the upper rad hose. It should be soft if there's no gas behind it and it will compress easily. If its ballooned because of gas you got da problem!
