How to Add Oil to MerCruiser Trim Cylinders

How to Add Oil to MerCruiser Trim Cylinders

Explore America's Campgrounds

The MerCruiser power trim feature allows the operator to raise and lower the drive unit for use in and out of the water. Power trim also allows the driver to raise and lower the bow of the boat by slightly modifying the angle of propulsion. This leveling action increases speed and performance. Power trim fluid is held in a reservoir inside the power trim pump or in a separate plastic reservoir near the pump. Maintaining proper levels of fluid is necessary for the trim system to operate properly.

Items you will need

  • Power trim fluid

  • Flat screwdriver

Open the engine compartment cover and locate the hydraulic trim pump in the lower rear area of the engine compartment. The unit will have two power trim hoses connected to it. Look for an optional plastic fluid reservoir next to the pump.

Place the stern drive into the "Down" or operating position using the trim controls at the driver's station.

Remove the fill screw from the top of the trim pump using a flat screwdriver. Check the fluid level. Open the cap of the translucent plastic reservoir next to the pump if the system is equipped with one. Check the fluid level using the fill mark on the side of the reservoir.

Open a container of power trim fluid. Most containers have a long neck with a narrow spout, eliminating the need for a funnel. Pour power trim fluid into the opening until the level reaches the bottom of the threads on the fill screw opening or the full mark on the reservoir. Replace the screw or cap.

Raise and lower the stern drive around ten times using the trim controls to remove any air bubbles from the system.

Remove the fill screw or cap and check the fluid level. Add more oil as needed and replace the fill screw or cap.


  • Contact a marine mechanic if the fluid has a milky color. This is an indication that water has contaminated the system.


  • You may substitute a good quality 10-30 or 10-40 motor oil for the power trim fluid.
Gone Outdoors