Oil pressure warning buzzer comes on after engine has been running for 20-30 minutes and engine slows down, I put throttle back to neutral and buzzer goes off and then speed up again for 3-5 minutes and buzzer goes off again. If I shut engine down, sometimes I can run for 30-40 minutes and nothing happens. 50 Hp Merc 4 stroke has plenty of oil. Sensor, pump, oil weight, filter? Where do i start?

Dave, October 2008

1st,filter because its cheap,2nd oil in case its diluted with fuel,3rd if its got an oil cooler make sure thats clear.find out if its got an oil themostat fitted,cause if that has failed in closed position, oil will over heat,thin out and lose pressure.lastly borrow,buy an oil pressure gauge screw in where buzzer is fitted,to see if engine has oil pressure,at cold, hot,idle and load.if you have a reasonable pressure,it must be switch.if not,oil pump,big ends or main bearings are worn

glen, October 2008