Engine winterisation is one of the most important services a UK boatyard offers. Done properly, it protects the engine through months of cold, damp conditions. Done badly — or not at all — it can result in cracked blocks, corroded components, and expensive repairs come spring.
This checklist covers the essential steps for winterising both inboard diesel and petrol engines, based on best practice from experienced marine engineers across the UK.
Cooling System
The cooling system is the most critical winterisation task. For raw water-cooled engines, drain the system completely and flush with fresh water. For closed-loop systems, check the antifreeze concentration — it should protect to at least -15°C for UK conditions.
Don't forget the raw water strainer, water pump, and exhaust system. Any trapped water can freeze and cause expensive damage. Run the engine briefly with antifreeze solution to ensure it reaches all parts of the cooling circuit.
-15°C
Minimum antifreeze protection level recommended for UK marine engines during winter storage
Fuel System
Fill the fuel tank to at least 90% capacity to minimise condensation. Add a fuel stabiliser to prevent diesel bug and fuel degradation over the winter months. Change the fuel filters and water separator — starting the new season with clean fuel is essential.
For petrol engines, the advice is different: either drain the fuel system completely or add stabiliser and run the engine to circulate it through the carburettor.
See This in Marina Yard Manager
Hull Blacking & Anode Replacement
NB Kingfisher — James Hartley
Full hull blacking with bituminous paint. Replace 4x zinc anodes. Pressure wash and degrease prior.
Try it free for 14 days — no credit card required
Start Free TrialOil and Lubrication
Change the engine oil and filter before storage, not after. Old oil contains acids and contaminants that can corrode internal components over the winter. Fresh oil protects the engine during its dormant period.
Don't forget the gearbox oil and stern gland greasing. Spray exposed metal components with a corrosion inhibitor, paying particular attention to the alternator, starter motor, and any exposed linkages.
Related Articles
Electrical System
Disconnect batteries and store them in a dry, frost-free location. A trickle charger or battery maintainer will keep them in good condition over winter. Check terminals for corrosion and apply petroleum jelly before reconnecting in spring.
For boats remaining connected to shore power, check the condition of the shore power cable and connections. Damp and cold can accelerate deterioration.
Documentation
Record everything you do during winterisation. A digital job card that logs each step, any issues found, and recommended spring actions creates a valuable record for the customer and for your yard.
This documentation also becomes your spring commissioning checklist — simply reverse the winterisation steps and address any noted concerns.
Frequently Asked Questions
When should boat engines be winterised?
Ideally as soon as the boat comes out of the water for winter — typically October or November in the UK. Don't leave it until the first frost; by then it may be too late.
Can I offer winterisation as a service package?
Absolutely. Winterisation packages are popular with boat owners and provide predictable revenue for yards. Price by engine type and include all fluids, filters, and labour.
Related Articles
Written by
Hamish Lowry-Martin
Founder & Lead Developer
With 30 years in IT and 20 years developing business systems, Hamish spent the last decade working closely with marinas and boat yards — watching first-hand how they struggle with outdated tools. That hands-on observation led to Marina Yard Manager.
Learn more about our teamReady to Streamline Your Yard?
Start your 14-day free trial. No credit card required.
Start Free Trial