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Power Trim
Operation
Trim Circuit - Up
When the trim up circuit is activated, the electric motor rotates the hydraulic pump. As the pump gears rotate, fluid is drawn
through a check valve and into the pump inlet. The fluid passes through a check valve, then passes through a pressure
operated (PO) check valve and to the bottom of the trim cylinder. The fluid pushes the cylinder piston out, trimming the engine
up. Oil, from the top side of the cylinder, returns through a passage in the cylinder wall to the inlet side of the pump. In this
mode, as the trim ram extends, up pressure increases to 16,080 kPa (2330 psi) and opens the up pressure relief valve. When
the engine is not running, the outboard may be tilted to the full up position by opening the manual release valve.
Trim Circuit - Down
When the down circuit is activated, the electric motor rotates in the opposite direction. As the pump gears rotate, fluid is drawn
through a check valve and into the pump inlet. The fluid passes through a check valve and to the top of the trim cylinder. The
fluid pushes the cylinder piston down and lowers the engine. Oil, from the bottom side of the cylinder, returns to the inlet side of
the pump. As the trim cylinder retracts to its limit, down pressure is limited to 7350 kPa (1070 psi) by an orifice in the down
pressure circuit.
Trail Over System
Should the outboard motor strike a submerged object, while in forward motion, hydraulic pressure on the top side of the
cylinder will increase to cause the impact relief valve in the trim cylinder to open. This allows the lower unit to trail over the
obstruction. The fluid in the top side of the cylinder opens the impact relief valve and flows into the cavity between the memory
piston and the cylinder piston. When the lower unit clears the submerged object, the thrust of the engine forces the engine back
down. As the cylinder piston is lowered, fluid trapped between the memory piston and the cylinder piston escapes through a
return check valve. Fluid below the memory piston is trapped in place, stopping the cylinder piston and returning the outboard
to its previous trim position.
Troubleshooting the Power Trim System
Preliminary Troubleshooting Steps
Determine if the problem is hydraulic or electrical related. Most often, if the electric motor operates, the problem is in the
hydraulic system. If the electric motor does not operate, the problem is in the electrical system.
IMPORTANT: Operate the power trim system after each check to see if the problem is corrected. If problem has not been
corrected, proceed with the next check.
1.
Check that the manual release valve is tightened fully, (clockwise).
2.
Check the power trim pump fluid level in the full up position. Fill if necessary. Refer to Checking Power Trim Fluid and
Purging Power Trim System in this section.
3.
Check for external leakage in the power trim system. Replace/repair the defective component if a leak is found. Maximum
acceptable power trim cylinder leak down is 25 mm (1 in.) within a 24 hour period.
Hydraulic System Troubleshooting
Condition/Problem
Trim motor runs; trim system does not move up or down.
Does not trim full down; up trim OK.
Does not trim full up; down trim OK.
Partial or jerky down/up.
Leaks down and does not hold trim.
Trim motor working hard and trims slow up and down.
Trims up very slow.
Starts to trim up from full down position when the down trim button is depressed.
Trim position does not hold in reverse.
Page 5B-10
Condition of Trim System
© 2016 Mercury Marine
Problem
1, 2, 5, 8
2, 4, 5, 11, 12
1, 2, 3, 4, 6, 10, 12
1, 3, 6
3, 4, 5
2, 7, 8, 9
1, 2, 6, 7, 8, 9, 10, 12
3, 4
2, 3, 4, 5, 12
90-8M0105568 eng MARCH 2016
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Troubleshooting
