Winterizing Boat Engines: Uk-Specific Steps For Smooth Sailing

As winter approaches, it's important to winterise your boat engine to protect it from freezing temperatures and potential damage. Winterising your boat engine is essential, especially if you're planning on leaving your boat moored up during the colder months. In this guide, we'll take you through the steps you need to take to ensure your boat engine is ready for the winter and performing flawlessly when the boating season returns. We'll cover everything from general cleaning and maintenance to specific engine winterisation techniques. So, whether you're a seasoned boater or a novice, read on to learn how to winterise your boat engine like a pro!

Drain the raw water system

Most diesel boat engines use raw water cooling, which needs attention before leaving for the winter. Raw water systems require full draining to prevent freezing and damage.

To start, close the water inlet valve or seacock. Then, disconnect a hose from the circulating pump, unless there is a dedicated tap or plug. If your boat is in the water, you will need to catch the water in a bucket to prevent it from entering the sea. Place a bucket under the exhaust pipe outlet to catch the water and dispose of it responsibly.

Next, refill the system with a strong solution of fresh antifreeze. This will protect the engine from corrosion. Start the engine and slowly pour the antifreeze mixture into the raw water strainer, which feeds the raw water pump. The mixture will be pumped throughout the raw water system and out through the exhaust.

Finally, run the engine to fully circulate the new solution. Simply draining the system is unlikely to remove all the water inside, which may then freeze and cause damage over the winter.

Change the engine oil

Changing the engine oil is a crucial step in winterising your boat engine. This is because oil can become contaminated with acidic by-products of combustion, which, if left inside the engine block, can cause expensive damage and shorten the engine's life.

Firstly, if you intend to change the oil, it is recommended to start the engine and let it warm up first. Warm oil flows more easily than cold oil when pumping it out. Before you begin, refer to your engine manual for specific actions required for your engine model.

Next, drain the old oil. Place a container underneath the engine to catch the old oil, then remove the drain plug. Allow the oil to drain out completely, then replace the drain plug. Now add new oil through the filler neck, ensuring you use the correct type and amount of oil for your engine. Check your operator's manual for these requirements.

Finally, replace the oil filter. This is important as a neglected oil system can cause expensive damage. Consider using flushing oil or a flushing additive during the oil change to help remove more of the contaminants.

Check the gearbox

When winterising a boat engine, it is important to check the gearbox or outdrive oil and replace it if it looks cloudy or milky. This is because the aluminium casings of most gearboxes can corrode, as can the intercooler pipe inside them.

To check the gearbox oil, you will need to consult the manufacturer's specifications and use a dipstick to check the oil level. The dipstick is usually unscrewed on the gearbox. For example, the Volvo Penta MS2 gearbox has the oil level checked with the dipstick unscrewed.

Over time, gearbox oil recommendations may change. For instance, the Volvo Penta MS2 gearbox has gone through several iterations, starting with multigrade engine oil, then using automatic transmission fluid, and now specifying GL5 fully synthetic gear oil. It is important to check that the oil you use complies with the manufacturer's recommendations. Ordinary vehicle oil can be used as long as it meets these specifications.

In addition to checking the gearbox oil, it is also important to check the alternator V-belt tension and other belt tensions. Belts that are left unused over the winter may become rusty, which can cause issues when the boat is used again.

Remove the air intake filter

Removing the air intake filter is an important step in winterising a boat engine in the UK. This is because, during winter storage, engine oil can drain away, leaving internal engine components exposed to scuffing and corrosion.

To prevent this, you should remove the air intake filter and block the intake with an oily rag to prevent rust inside. You can also squirt a little oil into the intake and turn over the engine (without starting it) to distribute the oil over the cylinder walls.

Be sure to place a warning about the blocked intake on the engine control panel to prevent anyone from accidentally turning the engine over.

Removing the air intake filter is just one part of the engine winterisation process. It is also important to change the engine oil, replace the oil filter, and fill the fuel tank to prevent condensation and the growth of diesel bugs.

Remove the batteries

Removing the batteries is an important step in winterising your boat engine. Batteries can be destroyed by cold weather, so it's best to take the time to ensure they are properly stored. If possible, remove the batteries and keep them in a warm, dry place over the winter. It is also important to keep them fully charged or topped up at least every four to six weeks. Batteries left uncharged for long periods may need to be replaced.

If you are unable to remove the batteries or if your boat is staying on its mooring, there are a few other things you can do to protect them. Firstly, leave them fully topped up and regularly recharged, as full batteries are less likely to freeze in sub-zero temperatures. You can also disconnect the mains power plug to prevent any issues with smart chargers. If you have solar panels, these can be used to provide a trickle of charge to keep your batteries healthy over the winter.

It is also important to remove batteries from any torches or electronic devices, as these can leak. Store them nearby, ready for next season. If you are leaving your boat moored throughout the winter, it is a good idea to double up your boat's lines so there is extra security if one fails.

Finally, make sure to keep a list of everything you have done to winterise your boat, so you can remember what to reverse when spring comes.

Frequently asked questions