300 hpdi water pressure problem

[charliedirks]

i own a 24 ft skeeter thats powered by a 300 hpdi.while running in gear,i get great water pressure up to 3500 rpm's.at 3500,it starts to drop and zeros at 4000.at somepoint the temp alarm then sounds.in neutral i dont have any problems.i can run the motor in neutral at 4000 rpm's and get 20-25 psi water pressure without any isssues or alarms.

[boats.net]

Replace water pump, check thermostats and clean pressure control valve.