Midseason Sterndrive Maintenance

It’s midsummer. Time for numerous maintenance tasks that will help ensure continued happy boating. Neglecting some of these might ruin your next trip. Neglecting others might cost you more dearly. You won’t necessarily need to haul the boat to perform these tasks, but a mask and snorkel can prove helpful if the boat’s kept in the water.

Of course, the first thing to check—and you should be checking this regularly—are the fluid levels. Start with engine oil, pulling the dipstick while the engine is cold and the boat is floating or level on its trailer or lift.

Next, check the gear-case lubricant. This would have been topped off at the start of the season, but sometimes air bubbles can ­prevent the oil from finding its proper level. Find the reservoir in your engine compartment and add the specified gear lube per your owner’s manual to the “full” mark. It’s normal to need to top off gear lube once or twice a season.

Related to gear-case oil levels, check your propeller shaft for fishing line. Look between the prop and the gear case for strands of line. If you haven’t knowingly run over fishing line, this might be sufficient. If you have run over fishing line, or just want to be ­completely sure, remove the prop and look. Fishing line can cut the seals, destroying your drive by allowing lubricant out and water in. Shaft seals with line cutters are standard on many sterndrive models.

Gear-case oil-level redux: If you do find fishing line around your prop shaft, haul the boat, drain the drive lube, and look for water. Let the drained lube rest in a clear glass jar, and any water will separate like salad dressing. Also, ­water-contaminated oil will come out looking whitish and frothy, like light coffee. Finding water, I suggest having the drive pressure-­tested. Then, change the seals and refill the lube ­before going back in.

Coolant level should be checked on freshwater-­cooled engines. With the engine cold, remove the pressure cap on the heat exchanger. The coolant level should be at the bottom of the fill neck. Replace the cap, and make sure it seats properly. Run the engine up to operating temperature, and check the level on the side of the recovery bottle. Add the specified coolant to the recovery bottle only when the engine is at operating temperature.

Read Next: Tips for Winterizing Your Sterndrive

Commonly called zincs, sacrificial anodes are also made from aluminum and magnesium. In any case, midseason is a good time to check the condition of these anodes, which sacrifice themselves to corrosion before the metal of the sterndrive gets eaten. Both drive and engine have anodes. Your engine’s  owner’s manual will show you the locations of the anodes. Adhere to the published replacement schedule. As a rule of thumb, replace an anode when it has lost half its mass.

Inspect your fuel filter by loosening the drain screw and draining fuel into a glass jar. Let the fuel settle. If there is water in the fuel, indicated by separation in the jar, replace the filter. Of course, also replace the filter if the specified hours have elapsed. Even for a scheduled change, dump the filter contents into a jar and look for excess water.

You’ll also want to look for physical damage to the drive and prop, be sure to lubricate all grease points per the owner’s manual, and check the belt ­tension. Finally, modern sterndrives have excellent self-protection systems and sensors built in. If you get an alert on the helm display, address it immediately.

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