How to recommission a marine engine after layup

Open the seacocks, check every fluid, inspect belts and hoses, fit a fresh impeller, then start and watch for water at the exhaust within seconds. The first start of the season is the most informative event of the boating year — it is where a winter of sitting announces itself.

Do this alongside, with help available, not on the way out through the heads.

The pre-start checks

Open the seacocks. Every one. Starting with the raw water seacock closed destroys an impeller in under a minute, and it is a genuinely common way to begin a season.
Check the engine oil. Level, colour, and whether it is milky. Milky means water got in over the layup and needs investigating before you start.
Check the coolant. Level and condition, with the engine cold.
Check the gearbox oil. Separate item, separate oil.
Inspect belts. Perished, glazed or cracked belts fail on first load.
Inspect hoses and clamps. Squeeze each hose — a hose that feels hard, spongy or crunchy has had its life.
Fit a fresh impeller if it sat compressed all winter, or at least inspect it. See how to change an impeller.
Clear the strainer, which may contain a winter’s worth of decayed weed.
Check the batteries — voltage, terminals, and whether they held charge.
Drain the primary filter bowl and look at the sample. Months of condensation collect there.
Look for rodent and insect damage. Chewed wiring and nests in air intakes are more common than owners expect.
Check the anodes, which have been dissolving all winter with the engine off.

Starting

Turn the engine over on the starter with the fuel off or the stop pulled, if your engine allows it, to circulate oil before it fires.
Start, and immediately look for water at the exhaust within seconds. If there is none, shut down.
Watch oil pressure come up promptly.
Listen. Note any sound that is new.
Let it warm at idle and watch the temperature stabilise.
Check for leaks around everything you touched — filters, hoses, the impeller cover.

Under load, before you rely on it

An engine that idles beautifully alongside can still fail under load. Before a real trip:

Run at cruise long enough for temperature to stabilise
Take it to full throttle briefly and confirm it reaches rated maximum rpm
Watch exhaust colour under load
Check gear engagement ahead and astern

A boat that has sat all winter with fuel in the tank is the classic candidate for filter blockage under load. That is far better discovered a mile from the berth than fifty.

Frequently asked questions

What should I check first after winter? That the seacocks are open. Starting with the raw water seacock shut destroys an impeller in under a minute.

Does the impeller need replacing after layup? It takes a set if left compressed for months. Many owners fit a new one at recommissioning as a matter of course.

Why is the first start so important? It is where a winter of deterioration shows — starting difficulty, smoke, leaks, and whether water reaches the exhaust.

My engine ran fine alongside but died on the first trip. Why? Very often fuel. Months of condensation and settled sludge reach the filters once motion stirs the tank.

Should I sea trial before a real trip? Yes. Run to cruise and briefly to full throttle close to home before relying on the engine.