Select Page

Why is engine winterisation so important? The answer is because an inactive boat engine needs to be protected from corrosion during the winter, caused by the rising humidity levels through the cold months and the salty coastal air. This applies whether the boat is left afloat or hauled out over the winter.

Assuming the boat is coming ashore, it is best to winterise the engine in two stages – firstly when the boat is still in the water so you can run the engine and secondly as soon as possible after the boat is secure in the boatyard. You need to allow a few hours to do the work. If other commitments prevent you from doing this within a couple of weeks of lift out, then it would be a good idea to make arrangements for a service engineer to do this for you as winterising should be carried out before corrosion can set in.

Diesel boat engine winterisation

Winterisation will vary a little from engine to engine, so it is always best to check the manual. The following is a basic guide that applies to most engines:

Stage 1 – boat in the water

  1. Run the engine until it is warm. Check all the fuel lines and engine cooling hoses for leaks.
  2. Stop the engine, drain the oil and change the oil filter. Note: it is much easier to pump warm oil out of an engine than trying to do it when the engine is cold.
  3. Refill the engine with new oil as recommended by the manufacturer.
  4. Run the engine to check the oil filter is properly sealed. Switch off and double-check the oil level is correct.
  5. Fill up the fuel tank to eliminate water condensation in the tank – this is also easier to do before lift out as you can come alongside a fuel berth. Water entering the fuel injection system can cause considerable damage. Added to this, water in the fuel stimulates the growth of bacteria which clogs up the filters. Smear some vaseline around the fuel filler cap threads to make it 100% watertight and easier to open in the spring – there is nothing more maddening than a seized fuel filler cap that will not budge.

diesel boat engine impeller

Stage 2 – in the boatyard

  1. Once ashore, protect engine cylinders by removing the injectors and spraying anti-corrosion oil into the cylinders while turning the engine by hand – plain engine oil can be used but special anti-corrosion oil is best. Use a ring spanner on the crank pulley to help turn the engine.
  2. Engines with closed circuit fresh water cooling systems should contain a 50:50 solution of antifreeze, or as recommended by the engine manufacturer. Drain the circuit and replace as necessary.
  3. Drain and flush the sea or raw water circuit with fresh water before filling it with an antifreeze mixture to protect it over the winter months. Do this as follows:

(i) Close the inlet seacock to the engine (engine stopped).

(ii) Disconnect the sea water inlet pipe and dip it into a bucket containing 50:50 antifreeze solution.

(iii) Start the engine (out of gear) and run for 10 seconds or so until the antifreeze is used up and can be seen coming out of the exhaust outlet.

(iv) Shut the engine off and reconnect the inlet pipe to the seacock.

  1. Remove the water pump impeller. The reason for doing this is that if the vanes remain in one position for months on end then they can become permanently deformed and more prone to failure.
  2. Most engines with raw water cooling have sacrificial zinc anodes to protect the engine from corrosion. On someboat engine zinc anode engines the anode is attached to a bolt which screws into one of the end caps of the heat exchanger. The easiest time to replace this is during winterisation. Check your manual to find out where it is.
  3. Slacken the alternator and water pump drive belts to extend their life.
  4. Protect the instrument panel and give the key switch a spray with WD40 or equivalent.
  5. Also protect the engine electrical circuit by disconnecting the connections and spraying them with WD40 or a water repellant spray.
  6. Clean and inspect the engine from all angles, making sure there are no water, fuel or oil leaks and that all the jubilee clips are in good condition and tight. Also clean the bilges to help reduce humidity and to make it easier to check for leaks that might develop.
  7. Lubricate the throttle and gear levers and linkages.
  8. Plug the exhaust outlet and air intake with rags to prevent any moisture from reaching the engine.
  9. Disconnect the engine battery and clean the terminals. Take the batteries home so they can be trickle charged and stored where they cannot freeze. Note that some owners store batteries on board if they have shore power for trickle charging and can keep the boat interior above freezing through the winter.

Repairing a leaking hull-to-deck joint

If you suspect a hull-to-deck joint has failed, then being absolutely sure where the actual leak is occurring is of prime...

Safe Skipper – crew management tips

Effective crew briefings are a vital part of the good on-board communication that helps everything to run smoothly on a sailing vessel at sea, whether it is cruising or racing.

Common medical emergencies at sea

A medical emergency aboard a boat at sea requires immediate attention to ensure the safety of the casualty and the crew in general. The skipper needs to know which crew members, if any, have had medical training or have a first aid qualification. All boats should carry first aid handbooks to help an untrained crew cope with a medical emergency.

Sailing to windward – how to take advantage of wind shifts

For most sailors, sailing upwind is the most exhilarating point of sail as you tack your way to your destination. Sailing to windward is a bit like zig-zagging your way up a mountain road through a series of hairpin bends – great fun but also calling for concentration and hard work.

Avoiding collisions at sea – how to stay safe on the water

Boats have many blind spots, including the headsails of sailing boats. Always keep a lookout, stay safe and remember that...

What boating skills should you have before you buy a yacht?

Many people dream of owning a yacht and sailing off into the blue yonder. What boating skills should you have before you buy...

Winch Servicing

It is not essential to service the winches when a boat is ashore, but if time allows I prefer to do this maintenance job when the boat...

Essential Knots: Figure of eight

Essential Knots: Figure of eight Use: Stopper knot, prevents a rope from being pulled through a hole e.g. through a block or...

Steel and Aluminium Hulls

The two metals used for hull construction are steel and aluminium. These are both very strong materials and will last a long time as long as they are cared for, which primarily means protecting steel boats from rust and aluminium boats from electrolytic action.

Hull inspection – the annual checks

With the boat ashore for the winter it is time to do a hull inspection - the annual checks. Are there any scratches and chips in the...

Keel design – options to consider when choosing a yacht

Keel design is constantly evolving and nowhere is this more apparent than in modern racing yachts such as the Imoca Open 60...

Essential boat engine checklist

Boat engine checklist Engine oil level check Even if you have checked it previously, confirming the engine oil level is up...

Seacock maintenance

If seacocks are always left open and neglected they can eventually seize which will prove a serious threat to boat safety should a connecting hose fail and the seacock refuses to close. There are three main types of seacock – ball valves, cone valves and gate valves.

Understanding tides

If you are used to sailing in tidal waters, you will know that tides can be both a benefit and a hindrance to the sailor. In many ways,...

Passage Planning Advice & Safety for skippers

Passage planning helps you to: • Decide where to go • Calculate how long it will take to get there • Avoid bad weather •...

Essential Boat Spares for Safety

  Boats Spares Tool kit What you carry in the boats tool kit will be useful for many boat repairs, but you might want...

Antifouling for leisure boats – Part 3

Antifouling is one of the least pleasant boat maintenance jobs to do, but it has to be done. The very worst job of all is removing the old antifouling as this can get seriously messy and is very hard work.

Boat engine basics

Boat engines come in all shapes and sizes and include inboards, outboards, petrol, diesel, electric and hybrid systems. Some engines are...

Keeping boat records and doing checks

A boat’s records should provide information about maintenance schedules, when major work was done and when equipment was replaced or added to the boat. Without this information you are left guessing when things are likely to need replacing in the future and also what the costs are likely to be.

Points of Sailing

The course on which a boat is sailing can be described by its angle to the wind, not to be confused with its compass...

Boat engine fuel system

If engines are installed and serviced correctly then most marine engines are very reliable, but one of the most important parts of the engine to check and service is the fuel system.

First Aid Afloat – jellyfish stings

  Wherever you are boating in the world I am sure you will be using a pilot guide to aid your navigation. Often in the...

ColRegs when sailing single handed

  Don’t neglect the Colregs when sailing single handed Sailing single-handed represents several challenges for skippers, not least how to...

Fire prevention on boats

  Fire prevention on boats - common causes of fire: • Smoking below decks • Galley cookers • Build-up of butane or...

Boating emergency – how to broadcast a MAYDAY emergency call

How to broadcast a MAYDAY emergency call   How to broadcast a MAYDAY emergency call if a vessel or person is in grave...