What happens if you don't winterize your boat?
I'm leaving my 28ft diesel cruiser afloat over winter and might use it once or twice. What could actually go wrong if I skip winterising it, and would an engine heater be enough?
Answer
If you don't winterise your boat, freezing water can crack engine components and burst plumbing, while months of neglect can cause internal corrosion, battery damage and mould. Check the engine's cooling arrangement first: boats afloat still need frost protection, and antifreeze in the sealed circuit does not protect the separate seawater circuit.
Frost can split engine components
Water expands as it freezes. Trapped inside a cylinder block, exhaust manifold, heat exchanger or seawater strainer, it can split the casting or housing. You may only spot the damage in spring, when water leaks into the bilge or mixes with the engine oil.
The vulnerable parts depend on the installation:
- Indirectly cooled inboard diesel: the sealed freshwater circuit normally contains coolant, but the seawater side still needs protection. Check coolant strength; colour tells you nothing about frost protection.
- Raw-water-cooled engine: water passes through the engine itself, so correct draining or antifreeze treatment matters especially here.
- Petrol sterndrive: the block, manifolds and coolers may have separate drain points. Follow the exact engine manual; opening one drain is rarely enough.
- Outboard: many drain their cooling passages when stored fully down and vertical. Leaving one tilted can trap water. Follow the manufacturer's storage procedure.
Coloured antifreeze at the exhaust does not prove every passage is protected. Dilution, trapped water and thermostat position all affect protection. Use the specified product and procedure, and collect discharged antifreeze for proper disposal.
A split strainer bowl might cost tens of pounds; a cracked manifold or heat exchanger can mean hundreds. Major engine damage can run into thousands. These are broad repair costs: access and labour can make a substantial difference.
Oil, fuel and plumbing damage
Change the engine oil and oil filter before laying up. Used diesel oil carries soot and potentially acidic contaminants. Leaving these against internal surfaces throughout winter encourages corrosion. Use the oil grade and quantity specified for your engine.
Fuel problems are less immediate than frost damage but can spoil the first spring trip. Petrol deteriorates during storage, while water contamination in diesel encourages corrosion and microbial growth. Check the water-separating filter and follow the engine maker's fuel-storage instructions. Adding a treatment does not remove existing water or sludge.
Freshwater plumbing needs separate attention. Water left in a pressure pump, cockpit shower mixer, calorifier or toilet pump can freeze and split it. Empty tanks and drain the system properly, or use a potable-water winterising product where the equipment instructions permit it. Never put engine coolant into drinking-water plumbing.