How should I winterise the engine on a Nauticat 33?

Winterise your Nauticat 33 by changing the engine oil and filters, protecting both cooling circuits against frost, and preparing the fuel system and batteries for storage. Identify the fitted engine and cooling arrangement first: many boats have a Ford Lehman diesel, but replacements and alterations mean the boat model alone cannot tell you coolant quantities or drain points.

Identify and service the engine

Read the engine identification plate and find the matching manual before buying oil, filters or antifreeze. Check whether it has indirect cooling, with a closed coolant circuit and seawater heat exchanger, or another arrangement. The procedure below assumes indirect cooling.

Inspect the engine compartment for coolant staining, seawater leaks, cracked hoses and loose hose clips. Repair leaks before laying up. A leaking circuit can lose its frost protection during storage.

1. With the normal cooling-water supply working, run the engine to operating temperature and check for leaks.
2. Stop the engine, pump out the warm oil through the extraction tube or dipstick tube, and replace the oil filter.
3. Refill with the oil grade and quantity specified for that engine. Run briefly and check oil pressure and leaks. Stop, let the oil settle and recheck the dipstick.
4. Check gearbox oil separately and change it if due; its lubricant specification may differ from the engine's.

Changing the oil before storage removes contaminated oil that would otherwise sit against internal surfaces all winter. Follow the engine manual's drain-plug torque and filter tightening instructions. There is no safe universal value for a Nauticat 33.

Protect both cooling circuits

Check the closed circuit first. With the engine cold, inspect the coolant level and test its frost protection with a tester suitable for that glycol type. Choose protection below the lowest expected local temperature. Replace coolant if it is overdue for renewal, rusty or unidentified. Do not mix incompatible coolant technologies.

Then protect the seawater circuit. This normally includes the strainer, pump, heat exchanger, any seawater-cooled oil coolers and the wet exhaust. Follow the engine manual's draining and flushing instructions, including separate cooler drain points.

Keep hands, clothing and hoses clear of belts. Ventilate against exhaust fumes and never remove a hot coolant pressure cap.

1. Close the seawater inlet seacock, clean the strainer and secure a suction hose from the pump supply into a bucket.
2. Flush with fresh water if the engine manual calls for it. Keep the pump supplied throughout; never let the impeller run dry.
3. Switch to marine winterising antifreeze approved for the components involved, mixed beforehand to the manufacturer's required concentration.
4. Run just long enough to draw the solution through the complete circuit. Stop before the bucket empties and catch the exhaust discharge for proper disposal.
5. Check the discharged mixture with a suitable tester. Colour alone does not establish frost protection, especially after dilution by trapped water.