Hello; I need advice on too hot Gill exhaust risers on one of my 500 HP engines. The motor runs too cool(100 degrees) while the risers are too hot. Water pressure seems to low (1 pound @ idle)and 5 pounds while running. This just started and I'm thinking I need to rebuild the impeller pump,and maybe a stuck open thermostat. Thanks for your input.

I would do both impeller and thermostat..also check the oil cooler for pieces of the impeller,even if theirs none of the blades missing on the impeller you take out..Still check it,also check the intake hose at the gimbal to drive,make sure i isn't collapsing also check the hose going from the gimbal to the sea water pump..

Probably a bad/broken impeller and part of it is stuck in the T-stat.

IMO 5psi running is low, 15psi at WOT is hwere I fell it should be.