eng o/h alarm goes off at high rpms only,,,i finally realized this has happened only in the summer,i guess because water is warmer,,alarm goes off and I wait 5 full minutes,alarm is off and I am good staying at 3400rpms,,,i ve had this problem for at least 5 years not realizing it only occurred in summer and previously have checked/reoplaced hd gaskets,cleaned water jackets,water pumps, thermostats,poppet valve grommet,also I had prop cleaned up prior to this problem and was told he cupped it alittle and my max rpms went down to 4500rpms,was 5400 i m pretty sure specs are 5500-6000,,,well I I m getting ready to due an ohms check again on sensors in hot water and use an ir temp gun on eng on a diagnosis run,,,,,,,,any suggestions thanks john