Saltwater Outboard Care: The After-Every-Trip and Monthly Routine

Mercury, Honda, Yamaha and Suzuki all say the same thing: flush with fresh water after every use in salt or brackish water. Mercury says flushing clears corrosive salt water from the cooling system. Do it the same day, before salt has time to dry inside.

• Flush port: connect the hose, turn it on, and flush for the time your manual gives (Yamaha's guide is 15 minutes). Keep the engine off unless your manual specifically calls for running it on the port. Some makers limit water pressure here (BoatUS reports Mercury's smaller four-strokes call for the tap only about halfway open), so check before you open the tap all the way. Many port fittings are plastic: thread the brass hose end on straight so you don't cross-thread it.
• Muffs or bag: remove the prop, fit the muffs over the water inlets (or fill the bag above the water pump level), turn the water on first, start in neutral and idle only. Yamaha says never rev the engine on muffs, and to shut down the engine before turning off the water. Many owners flush about 10 to 15 minutes; follow your manual.

Watch for the telltale (pee) stream while flushing. No stream means stop and check the hose and muffs. The freshwater flush guide covers this in detail.

Honda suggests flushing with its salt-removing product. Similar products from other makers dissolve salt that fresh water alone leaves behind. Use only as the label says, and don't mix products.

Owners often see videos of engines being "descaled" with vinegar or household lime removers pumped through the cooling system. That is a repair step for an engine that is already running hot from scale, not a routine. Don't push acids or household cleaners through your engine on your own; if your telltale is weak or the engine runs warm, have a dealer decide what it needs.

Leave the engine in the vertical (down) position for a few minutes after flushing so water drains out of the powerhead and lower unit, then tilt it up for storage.

Mercury says to lower the outboard to vertical before rinsing the cowl, because rinsing it tilted can let water into the air intake at the back of the cowl. Rinse the cowl, the mounting brackets, the trim rams and the cowl latches with low-pressure fresh water. Honda and Yamaha suggest a mild boat soap or the brand's wash, then a fresh-water rinse; Yamaha says not to use liquid dish detergent. Never spray water into the air intake, and don't use a pressure washer or jet nozzle on the engine: Mercury says high pressure can force water into electrical connections.

If salt has built up on the powerhead, or spray got under the cowl, Mercury and Yamaha both allow a careful rinse: cowl off, hose on low pressure with no nozzle, keeping water away from the air intake and the alternator. Rinse the inside of the cowl too. Let everything dry completely before refitting the cowl.

Honda recommends applying its corrosion inhibitor to everything under the cowl and to exposed metal monthly in salt water. Yamaha suggests spraying the external powerhead surfaces and electrical connections with its protectant. Mercury suggests a light coat under the cowl once the powerhead is dry, and a heavier-duty product on the gearcase, trim motor, exposed connections and other surfaces that run in the water.

The makers are specific about what to avoid:

• Belts and pulleys (timing and alternator belts): Honda and Mercury. A slippery belt slips.
• The alternator: Honda and Mercury.
• The air intake: Mercury.
• The oxygen sensor: Honda (on models that have one).
• Anodes: Honda and Mercury. A coated anode can't protect the engine.

Cover these with a rag or spray carefully. If your manual lists other spots, follow it.

Honda recommends waterproof marine grease on the lubrication points in your owner's manual monthly in salt water, because full grease joints keep salt water out. Typical points are the swivel bracket, tilt tube, steering link, tilt lock and the shift and throttle linkage. Wipe each fitting first, then pump until fresh grease appears. See the outboard grease points guide.

Anodes are the dull gray metal blocks, usually on the gearcase above the prop, the trim tab, the bottom of the transom bracket and sometimes on the trim rams. Yamaha says to check them every time you use the boat, scrub off any thin growth with a brush and soap so they stay in contact with the water, and replace them when about 50% gone, using quality factory-recommended parts. Mercury adds that anodes showing no wear can be a warning sign that corrosion is attacking something else. Never paint them.

Mercury also explains two things salt-water owners often miss: corrosion runs faster in warm water (a Florida boat eats anodes faster than one in Maine), and stainless steel near the aluminum gearcase, such as a stainless prop, powered trim tabs or aftermarket steering parts, speeds it up. If you switch to a stainless prop or add stainless hardware, check the anodes more often for the first few weeks.

Honda says if you moor in salt water, tilt the motor up so the gearcase is completely out of the water, which keeps marine growth from attacking its surface. Tilting up also stops anodes being used up while the boat sits. Store the outboard out of direct sun or under a breathable cover, as Honda suggests, to protect the paint and rubber parts. (Sterndrive owners are told the opposite; this advice is for outboards.)

Yamaha adds a trick for the trim rams, which sit in salt spray all the time: once the motor is tilted up, engage the built-in tilt lock (or fit an engine support), then press the trim down button until the rams pull fully back into the unit. That keeps all but the tips bathed in trim fluid instead of salt air; put a dab of marine grease on the exposed tips. The tilt lock is only for mooring and storage, never for trailering.

Honda warns that bare metal exposed to salt water corrodes, and the corrosion can spread under the surrounding paint. Check the gearcase, skeg and bracket for chips after each trip and touch them up with the maker's paint as soon as possible. Big blisters or white powder under the paint mean corrosion is already working; see the sacrificial anode guide and have a dealer look.

Honda recommends having the thermostat(s) and water pump serviced annually or every 200 hours in salt or polluted water, because salt shortens their life. A weak telltale stream or rising temperature between services is a sign to do it sooner. Typical; confirm in your manual. Watch for the opposite, too: Yamaha notes salt deposits (or a bit of debris) can hold the thermostat or pressure relief valve open, so the engine runs cooler than normal and never reaches its proper temperature. A temperature gauge that now reads lower than it used to is worth a dealer check.

Honda suggests a non-abrasive wax on the cowl to help salt rinse off. Yamaha recommends treating the rubber cowl seal with a silicone protectant so it stays supple. Log each flush, spray, grease job and anode check in BoatMend so the monthly items don't slip.