Maintenance Matters: Lower Unit Preventative Maintenance


Maintenance Matters: Lower Unit Preventative Maintenance

by Capt. Ted Lund


An outboard motor is one of the most significant investments any salt or freshwater boater can have. So it’s a good idea to take care of your engine — so it will take care of you.

There are a number of steps to preventative maintenance that boat owners will want to consider, but one of the most important is the lower unit, and it only takes a couple of hours.

It’s a good idea to start with an overall inspection of the lower unit, looking for damage, chips or leakage. Make a list of repairs needed. This is the perfect time to make sure you have the right gear case oil and the correct sacrificial anodes. You’ll want to make sure to complete the oil change and any repairs before any touch-up painting.

Ironically, water is Enemy No. 1 for lower units. If allowed to seep into the gear case, it will reduce the lubricating properties of the gear oil, promote corrosion of the gears and shaft leading to ruin for the lower unit. So you’ll want to start by draining the gear lube into a pan.


In order to make the most thorough check, run the engine to warm the oil up, then allow to rest in a full-down position so the lube and water separate.

Once the engine has rested for about an hour, remove the drain and vent plugs.

Use a drain pan to collect the oil; this allows you to see what is draining out of the gear case and also allows for easy disposal. A milky white froth is a sure sign that you have a problem.

If you do see signs of water or moisture in the gear case, take the unit to a Yamaha-certified mechanic to pressure test the lower unit. If you don’t see any signs of water intrusion, continue with the lube change.

This is also a great time to pull the prop and check the seals for damage and wear or fishing line wrapped around the prop-shaft.


If found, remove and dispose of properly to make sure it’s not an environmental hazard.

Next, (especially if you keep your boat in a water slip) you’ll want to check the sacrificial anodes on the engine in both fresh and salt water. These anodes help take the hit for corrosion caused by electrolysis. Replace any that are less than half of their original size and be sure to use only Yamaha-certified parts. Check the owner’s manual/service manual / for complete details and to make sure you know where all the nodes are located.


Although it sounds like a lot of work, servicing your lower unit is an easy job that can be done in the afternoon or evening prior to a big weekend outing.

All that’s left is to get out on the water.


For more helpful tips on maintaining your outboard investment or to learn more about the most-technologically-advanced four-stroke outboard motors on the water, visit


Original Source: Sportsmans




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