Thread: 115 mercury 2003

Originally Posted by Countryboy N.C.

Got an idea about what you are saying, but if you go look at the parts list on this motor, I can't see where there is a relief valve on the piston or in the side wall. it pumps fluid in to raise the motor up, so if I have it up and then it goes down on its on, then something is leaking by, right?

There are check valves in the piston that are there for excessive pressure relief purposes. The little holes in the piston on the diagram are where they are located. They are not available for purchase separately and are not pointed out. The relief valve in the 'tilt' circuit is in the valve body. It's channeled through one of the ridges that run up along the side of cylinder. In the cylinder wall is a small hole that opens into that circuit. Once the piston rises to the point that fluid can access that circuit, you loose the ability to hold high pressure. Which means you're at the top of the 'trim' point. If you were to raise the motor beyond that point while idling around and then apply the throttle, the motor should drop to the top of the trim position. If it's dropping down below that, then yes, there is something not right with the system.
From my experience, one of two things usually bring about trouble with the hydraulic side of the system. Either a high speed impact has caused a spike in working pressure and damaged a seal, o-ring or check valve. Or prolonged use of the system has worn the cylinder wall down and cast fine metal shavings into the system which usually leads to the check valves not seating properly.

Originally Posted by sliderman

There are check valves in the piston that are there for excessive pressure relief purposes. The little holes in the piston on the diagram are where they are located. They are not available for purchase separately and are not pointed out. The relief valve in the 'tilt' circuit is in the valve body. It's channeled through one of the ridges that run up along the side of cylinder. In the cylinder wall is a small hole that opens into that circuit. Once the piston rises to the point that fluid can access that circuit, you loose the ability to hold high pressure. Which means you're at the top of the 'trim' point. If you were to raise the motor beyond that point while idling around and then apply the throttle, the motor should drop to the top of the trim position. If it's dropping down below that, then yes, there is something not right with the system.
From my experience, one of two things usually bring about trouble with the hydraulic side of the system. Either a high speed impact has caused a spike in working pressure and damaged a seal, o-ring or check valve. Or prolonged use of the system has worn the cylinder wall down and cast fine metal shavings into the system which usually leads to the check valves not seating properly.

Thanks, I see what you are saying, I'll change the o rings first, if that dont fix the problem then I'l move to the check valve.