How to Change Sterndrive and Outboard Gearcase Lubricant

Most sterndrive and outboard manufacturers advise you to change the gearcase oil in your lower unit every 100 hours or once a year. Clean oil is critical for protecting the heavily loaded gears in your lower unit and preventing expensive damage. Servicing the lower unit is a simple job that you can easily do yourself.

 The Right Stuff

Check with your engine manual for the correct type and quantity of lubricant for your engine. There are different specs and weights for gear-case lubricants.

 Go With Flow

Run the engine for a few minutes on a flusher to warm up the lube, particularly if it is cold outside. A heat gun, hair dryer or halogen work lamp applied judiciously will also warm up the lube quickly so it will flow well.

 Neat and Tidy

Make sure the drain pan is positioned under the lower drain screw so lubricant won’t splash out onto the ground. A makeshift pan, made by cutting the side out of a gallon jug of motor oil or antifreeze, works well and even has a spout for pouring off the used oil.

 Fill ’er Up!

Remove the vent (top screw) and then remove the drain (bottom screw). It’s important to use a correctly sized (big) screwdriver to avoid stripping the head of the tightly torqued screws. Once they are out, be patient waiting for the oil to drain. Be Quick, Now!

Insert the lube spout into the lower (drain) hole and fill. When lube oozes out the vent (top) hole, you know it is full. Replace the vent screw while keeping the spout in place. Quickly replace the drain screw.

 New, New, New

Use new gaskets when reinserting the drain/fill and vent screws. These gaskets are rigid, and it may prove helpful to screw them on by gripping them gently but firmly with pliers.

 Patience

Air bubbles can form if you try to fill too quickly, which may starve the upper drive-shaft bearing of lubricant. Spin the prop a bit while filling to help expel the air pocket. Once oil oozes from the vent the first time, wait a few minutes, then pump some more in.

Quick Tip: While you’re changing the lube, remove the propeller and check for fishing-line snarls behind the thrust washer; grease the prop shaft and reinstall the prop.