Maintaining outboard motors between sailing trips

Why the time between trips does the damage

Outboards rarely fail because of the hours they run. They fail because of the weeks they sit still. Salt water left in the cooling passages dries into crystals that eat aluminium. Petrol left in a carburettor bowl evaporates, varnishes, and blocks the tiny jets that make a two-stroke or four-stroke start on the first pull. An impeller that has been squeezed against the same spot in the pump housing for a month develops a permanent set and never pumps properly again.

If your tender lives on a mooring, a trailer, or a dinghy rack at the sailing club, you are asking a lot of it. The good news is that a proper between-trips routine takes about ten minutes and will add years to the engine's life.

Flush with fresh water before you do anything else

This is the single most valuable thing you can do for a saltwater outboard. Do it while the engine is still warm from the run back to the harbour, because the thermostat will be open and fresh water will reach the whole block rather than just the top of it.

• Use flushing muffs on the lower unit if the engine has a standard water intake, or drop the leg into a tub or wheelie bin of fresh water if the muffs won't seal. A dustbin works beautifully for small tenders.
• Run for five to ten minutes at a fast idle, with the tap on enough that water spills around the muffs. Never run an outboard dry, even briefly.
• Watch the tell-tale the whole time. A strong, steady stream is what you want. A dribble or nothing at all means you should stop immediately and investigate.
• Wash the outside while you're at it. Rinse the cowling, the leg, and around the tilt brackets, then dry and give the powerhead a light spray with a water-displacing corrosion inhibitor, avoiding the electrics and air intake.

If you have a carburettor two-stroke and won't be out again for a fortnight or more, shut the fuel tap and let the engine idle until it dies. That empties the float bowl. Do not do this with a fuel-injected four-stroke, which should be left with fuel in the system and a dose of stabiliser instead.

Impellers, thermostats and hidden anodes

The impeller is a rubber paddle wheel inside the gearcase that pushes cooling water up to the powerhead. It is cheap, it is easy to change, and it is responsible for a huge share of breakdowns afloat.

Replace it every two or three seasons as a matter of course, and annually if you run in sandy or silty water, or if you habitually beach the tender and run the leg through mud. Warning signs before it fails: a weak tell-tale, overheating at low revs that clears when you open the throttle, or steam in the exhaust.

While the gearcase is off, check the thermostat, the pump housing for scoring, and any small anodes fitted inside the cooling passages or on the powerhead. A few manufacturers fit sacrificial anodes that are easy to forget. If one is more than half consumed, it has stopped protecting anything.

Fuel: the biggest cause of springtime frustration

Modern UK pump petrol contains ethanol, which absorbs water from the air and goes stale in as little as a month in a vented tank. In an outboard, that means difficult starting, rough running, and gummed jets.

• Use a fuel stabiliser in every can you fill, not just the ones going into winter storage.
• Choose the freshest fuel you can and buy it in quantities you'll use within a few weeks. Supermarket petrol that has sat in a can since spring is not a bargain.
• Store cans sealed, full, cool and out of direct sunlight. A part-full can breathes with every temperature change and condenses water inside.
• Inspect fuel lines and the primer bulb for hardening, cracks or a sticky feel. Ethanol attacks older rubber, and a perished line will suck air and cause a lean, hot-running engine.
• Check the inline filter and any water-separating filter, and drain the carburettor bowl before a long lay-up.

Gearcase, propeller and the moving parts

Drain a little gear oil into a clean jar at the end of the season. If it comes out milky or grey, water is getting past a seal and the gearcase needs attention before it becomes a costly repair. Grease the propeller shaft splines annually, check the prop for dings and bent blades, and look for fishing line wrapped behind the prop, which is a classic cause of seal failure.

Replace anodes once they are half gone, and make sure the mounting surfaces are clean bare metal so they actually make contact. Then work through the small things: lubricate the tilt and trim rams, grease the steering tube and throttle linkages, check the cowling gasket, and inspect the spark plugs for a healthy biscuit-brown colour. Carry a spare plug, a shear pin or split pin, and a basic tool roll aboard.

A ten-minute routine when you come ashore

• Flush with fresh water and check the tell-tale.
• Shut off the fuel and, if carburetted, run the bowl dry.
• Rinse the exterior, dry, and mist the powerhead with inhibitor.
• Tilt the engine up so the leg drains fully.
• Top up or drain fuel according to how long you'll be away, always with stabiliser.
• Wipe down the cowling and stow the cover loosely so air can circulate.

Do that and your outboard will reward you with a first-pull start on a grey Saturday morning when everyone else on the pontoon is pulling a cord and swearing.