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.

Care of boat batteries

Boat batteries need to be kept properly charged, which means never allowing the batteries to discharge below 50 per cent of their total charge. As well as the batteries themselves, keeping a boat’s charging systems in good shape will also help to keep batteries topped up to a higher level of charge.

Common marine electrical problems

Most problems with marine electrical systems arise from four possible sources, a lack of maintenance, a poor standard of initial installation, insufficient battery capacity, or ineffective charging systems.
Water ingress is a frequent issue – salt water can corrode contacts very quickly. If connections are not scrupulously clean – or are loose – resistance will be increased, resulting in progressively reduced power.

How to ensure your boat is in proper working condition

In this article Eva Tucker from Volvo Penta presents a handy check list of all the things that you need to check regularly in order to make sure that your boat is in a seaworthy condition. Including maintenance, safety gear and electrical checks.

Hourly Checks when sailing or motoring

  Hourly Checks Get into the habit of carrying out these checks and both yourself, your crew and your boat will be...

How to tackle osmosis

Many owners of old GRP boats live in fear of osmosis, but what exactly is osmosis and what can be done about it? Osmosis comes about...

Stress cracks on GRP boats

It is quite common to find cracks in the gelcoat when inspecting the deck and superstructure of a GRP boat. It is important to differentiate between a gelcoat crack and a scratch.

Keel maintenance and Repair – Part 2

If you have ever witnessed a boat colliding with a rock or other submerged obstacle you will know that there is an almighty thump and the whole boat shakes and judders. While such hard groundings seldom result in catastrophic keel failure, something has to give and even the sturdiest keels can easily be damaged by such an impact.

A five day sailing cruise of the Solent, UK

Welcome to our virtual Solent sailing cruise – a five day sail in the south of England from Bosham Quay in Chichester...

Dag Pike’s Boat Survey

We're really pleased to be working with Dag Pike on some great new apps for iPhone & Android. Here'a a bit more about the first app: Dag Pike's...

Wooden Hulls – Part 1

Traditional wooden boats have a plank on frame construction, a centuries old boat building method that is still in use today. Variations of the traditional method include carvel, clinker and strip planking, which all relate to the way the planking is attached to the frame.

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...

Boat interior varnishing

Most boat interiors have a combination of varnished and painted surfaces including solid wooden joinery, plywood laminates with thin hardwood veneers and glass reinforced plastic. When making your assessment of what you are going to do, bear in mind that the varnishing process consumes a lot of time, especially if the existing surfaces are in poor shape.

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.

Marine engine oil system maintenance

The regular maintenance of a marine diesel is key to preventing engine failure at sea. This means doing regular checks of the fuel, cooling, electrical and oil systems.

Peer to Peer yacht charter – How can you monetize your boat?

There is a growing trend in peer to peer yacht charter. How does it work? People already rent rooms, cars and bikes from one...

Capsize – understanding the risks

A skipper should know how their boat will cope with rough seas. By working within known limits and understanding the risks,...

Cleaning & polishing gelcoat topsides

The gelcoat topsides of a GRP boat can be pampered and restored to their former glory relatively easily when it is ashore. Gelcoat is only a very thin outer layer of the hull, often less than 1mm thick, so you should avoid cleaning it with highly abrasive cleaners, or an-ything that could potentially damage its surface.

Wooden Hulls – Part 2

It is important to ensure the essential hull maintenance of a wooden boat is done, even if you are paying others to look after your boat for you. The priority is to prevent rot from taking hold. The protective layers of paint and varnish over wood are far more critical than on GRP boats, where the topsides are painted more for cosmetic reasons.

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...

First Aid Afloat – how to deal with a fracture at sea

First Aid Afloat A closed fracture does not break through the skin. An open fracture is when the bone punctures it. A...

Keel maintenance and repair – Part 1

Keels are designed to act as underwater foils that generate lift as the boat moves through the water, counteracting the leeward force of the wind and enabling the boat to sail closer to the wind. Keel maintenance and repair is essential for the performance of your boat.

Safety at sea principles

Safety at sea is not as simple as just spending money adding shiny new emergency equipment such as liferafts, danbuoys, distress flares, EPIRBs and so on.

Boat decks and superstructure

The deck of a boat is constantly exposed to the elements and should be inspected on an annual basis. Particular attention needs to be given to the overall condition of deck fittings such as the stanchions, cleats and chainplates.

Cleaning & polishing painted topsides

The gelcoat topsides of a GRP boat can be pampered and restored to their former glory relatively easily when it is ashore. Gelcoat is only a very thin outer layer of the hull, often less than 1mm thick, so you should avoid cleaning it with highly abrasive cleaners, or an-ything that could potentially damage its surface.

Boat gas system maintenance

There are correct types of hose for marine plumbing, sewerage, exhaust, cooling and gas and all hoses should be checked regularly for wear and deterioration.