Diesels Afloat co-author Callum Smedley explains how best to ready your yacht's engine for the winter season

When laying up for the winter, it’s important to prepare your diesel engine so it won’t suffer while remaining unused for an extended period. It helps to make a list of everything you do when laying up the engine, then using that list when you recommission the engine to ensure everything is reinstated correctly.

Remember to keep the fuel tank full in the winter to minimise condensation, and carry out a full service of the engine and gearbox before lay-up, giving them a quick run so the new, clean oil coats all of the inside moving parts.

Cooling system

If you have indirect cooling, it’s a good idea to flush the seawater part of the system. Disconnect the hose, put it into a bucket of fresh water and antifreeze, then run the engine until this bucket is empty. Seawater remaining in the system can freeze in very low temperatures, and simply draining the system is not always fully effective.

Stuff rags into the intakes and exhausts to keep debris, creatures and damp out

Air system

Disconnect the exhaust hose from the engine and check its condition. Remove the air cleaner, spray water-repellent oil up the exhaust and air intakes, then seal with plastic bags to prevent damp air entering. Check the exhaust injection bend for carbon build-up and cracking, and check the exhaust pipe hose for delamination and any build-up of carbon. If the boat is to remain afloat, block the exhaust where it leaves the hull, or reconnect the exhaust to prevent water flooding the boat, otherwise leave it open to ventilate the hull.

Ventilation & heating

To help prevent condensation, open all access panels to the engine compartment to allow ventilation. If mains power is available, use a low-powered tubular heater in the engine compartment. A dehumidifier, although relatively expensive to buy, is cheap to run and will help protect your investment through the long winter.

A fuel filter with a glass bowl lets you quickly see if there is water in the diesel. Photo: Matt Sheahan

Out of the water

If the boat is to be laid up ashore, clean and antifoul the propeller, and check and renew your anodes if necessary. You should also prime and antifoul the stern gear. If the stern gear is aluminium, ensure you use compatible antifouling paint. Finally, ensure that raw-water-cooling intakes are unobstructed.


Work methodically back through the list you made when you laid up the engine. Check the battery level, all its connecting cables, and its voltage, which should be around 12.5V. Top up the batteries with distilled water, if necessary. The engine should have been serviced before lay-up, but you still need to check the oil levels.

The coolant level also needs to be checked, and a sample drawn from the bottom of the fuel tank to ensure there’s no water in the fuel. Test run the engine and check all of the systems before setting off out to sea. The engine’s alignment should then be checked a couple of weeks after launching as the hull will have settled back into its natural floating shape.

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