yamaha water pressure drops off

[hlturner]

help! i have a 1996 yamaha 150hp that over heated one afternoon. i changed the water pump and thermostats. at idle i have good water pressure and up to around 2200 rpm, when i accelerate to get up on top the pressure slowly drops off to zero with minimal water peeing out of the motor. i can idle all over the bay with no alarm, but it

 

[Captain Paul]

Re: yamaha water pressure drops off

did you clean the pressure relief valve? I don't know if that is your problem, but it is a cooling function

 

[Ray Neudecker]

Re: yamaha water pressure drops off

Also may mean you have blown a head gasket when it overheated. Try a compression test.

 

[hlturner]

Re: yamaha water pressure drops off

thanks for the replies, where is the pressure relif valve? i never knew i had one... thanks, hlturner

 

[Captain Paul]

Re: yamaha water pressure drops off

boy, this item is mentioned a lot. On my 150 yammi, it is on the bottom of the power head, in the center, on the back side, looks like a thermostat housing, has a pretty good size tube on the lower end of it. When you take off the cover, mine has a spring that holds the valve in place, the valve mates up to a rubber grommet on the block. Make sure the valve is clean and moves freely against the grommet. Mine had poo on it and did not move freely. I de-pooed it.

 

[hlturner]

Re: yamaha water pressure drops off

thanks for the info capt paul, i will conduct a search...(again greatly appreciated)

 

[rodbolt]

Re: yamaha water pressure drops off

look close at compression, what caused the first overheat ? your symptoms dont indicate a pressure valve issue but its part of the cooling system maint.

 

[gejandsons]

Re: yamaha water pressure drops off

I had a friend who installed the strainers on the water intake backwards. This caused the water pump to loose its prime , since the strainers are directional. this of course would not be the cause of the original over heat, but will cause you to loose psi when moving forward.