Winterizing the Tender Outboard: Storage and Preservation

A small outboard that is flushed with fresh water, has its fuel dealt with deliberately, gets fresh gearcase oil and is stored upright in a dry place will start in spring. One that is lifted off the transom in October and dropped in a corner of the garage with half a tank of petrol in it will not, and the reason is almost always the carburettor, where fuel left standing for five months turns to varnish and blocks passages measured in tenths of a millimetre.

Outboard winterisation is a two-hour job that belongs alongside the rest of the end-of-season layup, and it that prevents the single most common spring frustration among cruising owners, and the tender is exactly the piece of equipment that gets neglected because it feels peripheral. It is also the piece you will want working on the first weekend of the season. What follows applies to the small four-strokes that serve most cruising tenders, with notes on two-strokes where they differ. The inboard auxiliary is a separate job with its own procedure, covered in winterising a sailing boat motor.

Flush the cooling system

Salt water in a cooling passage does not stop being a problem when the engine stops running. It sits in the block and the exhaust passages, evaporates, and leaves salt crystals that build into deposits and drive corrosion all winter. Flushing is the single most important step and it needs to happen before anything else.

Use a flushing attachment on the water intake or a tank large enough to submerge the leg, run the engine at idle for ten to fifteen minutes on fresh water, and check throughout that the telltale is producing a steady stream. If the telltale is weak or intermittent, the impeller or the passages need attention, and finding that out in October is far better than in June. Some owners run a salt-removing solution through at this stage, which does no harm and helps on engines used exclusively in salt water.

After flushing, let the engine drain fully in the upright position before it goes into storage. Water left in the block and then frozen is one of the few ways to crack a small outboard, and it is entirely avoidable.

Dealing with the fuel

This is where most spring starting problems are made, and there are two valid approaches. Choose one deliberately rather than doing half of each.

Run it dry

For a small portable outboard with a separate tank, disconnecting the fuel line while the engine is running and letting it consume everything in the carburettor bowl is the simplest and most reliable method. The engine stops when the bowl is empty, and there is then no fuel left to degrade. Follow it by draining the tank itself, or by taking the tank home and using the petrol in something else.

Stabilise and fill

The alternative is to add a fuel stabiliser to fresh petrol, run the engine long enough for treated fuel to reach the carburettor, and store the tank full to reduce condensation in the air space. This suits engines with integral tanks and fuel injection, where running dry is neither easy nor recommended. Stabiliser is not optional in this approach: modern petrol with an ethanol content degrades noticeably within a few months and ethanol also absorbs water, which then separates out and sits at the bottom of the tank.

What not to do

Do not leave untreated petrol standing in the carburettor for the winter, which is the default outcome of doing nothing. Do not store the tank half full, since the air space above the fuel is where condensation forms. And if the engine has been running badly on old fuel already, deal with that now rather than storing the problem.

Oil, gearcase and lubrication

Engine oil, four-strokes

Change the engine oil and the filter before storage rather than after. Used oil carries combustion acids and moisture, and leaving those in contact with bearing surfaces for five months does real damage. Run the engine briefly first so the oil is warm and flows out carrying the contaminants with it, then refill with the grade the manufacturer specifies.

Gearcase oil

Drain the gearcase and look carefully at what comes out. Clean oil of the expected colour is good news. Milky or creamy oil means water has been getting past the seals, and metallic glitter means something inside is wearing. Either finding is a reason to have the leg looked at over the winter, and both are far cheaper to address then than in season. Refill from the bottom drain until oil appears at the upper vent, which is the only way to fill a gearcase without leaving an air pocket.

Fogging and greasing

Fogging oil sprayed into the intake while the engine runs coats the cylinder walls and prevents surface corrosion over a long layup. It is standard practice for two-strokes and worthwhile for four-strokes stored in unheated spaces. Remove the spark plugs afterwards, put a small amount of oil into each cylinder, turn the engine over by hand a few times to distribute it, and refit the plugs. Then grease every grease point on the leg, the steering and the tilt mechanism, and lubricate the throttle and shift linkages.

Getting the outboard off the boat

A small outboard is heavier and more awkward than it looks, and the transfer from the pushpit bracket or the tender transom to the dinghy and then to the pontoon is where they get dropped. Use a halyard and a simple tackle rather than muscle: the mechanical advantage makes the lift controlled, and control is what you want when the boat is moving. The same rig you would use for hoisting the tender aboard works for the engine, and it lets one person manage the job safely.

Keep the engine upright throughout. Laying an outboard on its side, particularly on the wrong side, allows oil or water to migrate into the cylinder or out of the breather, and it is a common cause of a smoking engine on first start. If it must be laid down for transport, follow the manufacturer's specified side and keep it there for as short a time as possible.

Storage position and place

Store the outboard upright, on a proper stand or bracket, in a dry and ventilated place. Upright allows any remaining water to drain out of the leg rather than sitting in it, which is the specific concern in a hard frost. A garage wall bracket is ideal; a corner of a damp shed on the floor is not.

Cover it loosely to keep dust off, using something breathable rather than a sealed plastic bag, which traps condensation against the powerhead in exactly the way a sealed cover does on deck. Remove the propeller if it is easy to do so, both to check the shaft for fishing line wrapped behind it, which is a routine finding, and to grease the shaft splines before refitting. If the engine has an integral fuel tank and you have stabilised rather than drained, check on it midway through the winter.

The tender itself

While the engine is being dealt with, the tender deserves the same attention and takes far less time. Wash it inside and out with fresh water, particularly the inflatable seams and the transom joint, and let it dry completely before folding, since an inflatable folded damp will grow mould and the mould stains permanently. Deflate it partially rather than completely if it is being stored assembled, and keep it out of sunlight and away from rodents, which nest in folded inflatables as readily as in sails.

Check the valves, the painter, the oars and the repair kit while it is out, and note what needs replacing. Store it flat and loosely folded rather than compressed into a tight bundle, and if there is space, storing it lightly inflated is better still for the fabric.

Two-strokes and electric outboards

Two-strokes

The procedure is broadly the same with three differences. Fogging matters more, because there is no oil film sitting in a sump to protect the internals, so a generous application through the intake while the engine runs is standard practice rather than optional. There is no engine oil or filter to change, since lubrication comes from the fuel mixture, but the gearcase oil still needs draining and inspecting exactly as on a four-stroke. And pre-mixed fuel degrades in the same way as straight petrol, so it still needs to be run out or stabilised rather than left in the carburettor.

Electric outboards

An electric outboard removes the fuel problem entirely and replaces it with a battery problem, which is more forgiving but not trivial. Store the battery at the state of charge the manufacturer specifies, which for most lithium chemistries is a partial charge around half capacity rather than full or empty, and keep it somewhere that does not go below freezing. Rinse the leg and the motor housing with fresh water as you would any outboard, dry the connectors thoroughly, and protect them with a suitable contact grease. Check the anodes, which electric legs have just as petrol legs do and which owners frequently forget.

Anodes, seals and the things people forget

The outboard has sacrificial anodes, usually one on the leg and sometimes another inside the cooling system or on the transom bracket, and they are doing the same job as the anodes on the hull. Inspect them at layup and replace anything more than about half wasted, because a depleted anode over a season means the corrosion has been going somewhere else instead. Do not paint them, and make sure the mounting face is clean metal so the electrical contact actually works.

Check the water intake screens for weed and silt, since a partially blocked intake is a common cause of the weak telltale that owners attribute to a failing impeller. Look at the tilt and steering pivots for play, and at the transom clamps for corrosion and for a clamp handle that no longer tightens fully, which is how outboards end up on the seabed. If the impeller has more than a couple of seasons on it, the winter is the right time to replace it: it is a cheap part and a straightforward job when nobody is waiting for the tender.

Recommissioning in spring

The work done in the autumn makes the spring start almost uneventful, but a short sequence is still worth following. Check the oil level and look for any sign of water in it. Refit the propeller with fresh grease if you removed it. Connect fresh fuel rather than anything left over from last year, even if it was stabilised, because a new season is worth a clean start. Then run the engine on a proper water supply, never dry, and watch the telltale from the first seconds.

Let it warm up and listen. An engine that was fogged will smoke for a minute or two as the oil burns off, which is expected. What is not expected is a weak telltale, an irregular idle that does not settle, or any milkiness on the oil dipstick, and each of those means stopping and investigating rather than pressing on. Fifteen minutes at this stage confirms the engine is genuinely ready, which is worth knowing before the tender is the only thing between you and the shore.

Common mistakes

Leaving untreated fuel in the carburettor over winter is the first and by far the most common, and it is what produces the engine that will not start in April. Skipping the freshwater flush is the second, and it leaves salt in the cooling passages for five months. Storing the engine on its side lets fluids migrate where they should not. Changing the oil in spring rather than autumn leaves acidic used oil in contact with bearings all winter. Storing under a sealed plastic bag traps moisture. And leaving the gearcase oil unchanged means you never find out that the seals have been letting water in until the leg fails.

Frequently asked questions

Should I run the outboard dry or fill it with stabilised fuel?

For a small portable engine with a separate tank, running it dry is simpler and more certain, because there is then nothing left to degrade. For engines with integral tanks or fuel injection, stabilised fuel in a full tank is the right approach and running dry may not even be possible. What matters is committing to one method properly rather than partially doing both.

Do I need to start the outboard occasionally over winter?

No, and doing it badly is worse than not doing it. A brief run without a proper water supply damages the impeller, and a short run that does not reach operating temperature puts moisture into the oil and unburnt fuel into the cylinders without burning it off. A properly winterised engine is better left alone until spring.

Can I store an outboard outside?

It is much better not to. Outside means UV on the cowling, condensation cycles every night and, in a hard winter, freezing water in whatever passages did not drain. If there is genuinely no indoor space, store it upright, well covered with something breathable, off the ground and out of direct sun, and accept that it will need more attention in spring.

What does milky gearcase oil mean?

Water has been getting into the gearcase past a seal, usually the propeller shaft seal or the shift shaft seal. It needs the seals replaced before the engine is used again, because water in the gearcase corrodes the gears and bearings and will eventually destroy the leg. Finding it in October means it can be fixed calmly over the winter.

Should the propeller come off for storage?

It is worth removing it if you can. It lets you check for fishing line wrapped behind the propeller against the seal, which is extremely common and quietly destroys the seal, and it lets you clean and grease the shaft splines. Refit it with fresh grease and the correct torque on the nut, and replace the split pin rather than reusing it.

The short version

Flush with fresh water for ten to fifteen minutes and let the engine drain upright. Deal with the fuel deliberately: run it dry, or stabilise and fill, but never leave untreated petrol standing in the carburettor. Change the engine oil while it is warm and the gearcase oil while you can still inspect what comes out. Fog the cylinders, grease the linkages, and lift the engine off with a tackle rather than by hand. Then store it upright, indoors, loosely covered with something that breathes. Wash and dry the tender at the same time and store it loosely folded, because an inflatable put away damp is an inflatable that comes out stained.