Mercruiser & Volvo Penta Marine Engine Winterising Tips

Winterising their marine engine is the most important maintenance job the boat owner can perform. When completed correctly, preparing the boat for sea the following season will be trouble free without any nasty surprises. Winterising greatly extends the life of the engine by protecting the components from corrosion, freezing and contamination.

Like Mercruiser and Volvo Penta, Repower Marine’s warranty does not cover damage caused by freezing or incorrectly performed winterisation. You may want to consider having a suitably qualified marine engineer to complete the work.

There is a misconception that the marine engine drain system is a substitute for full winterisation. Draining the system down may not offer adequate protection against freezing during a harsh winter, and pockets of trapped water can be all it takes to cause the failure of your exhaust manifolds or engine long block.

Below is a list of recommended end of season maintenance jobs:

Steering and Shifting Cables

If the steering cable has grease fittings, lubricate them with a grease gun, with the steering cable fully retracted into the cable housing. Use engine oil to lubricate all the steering system and throttle/shift system pivots. Apply a thin coat of rust inhibitor (WD40) on your steering and control cables.

Flushing the Engine and Sterndrive.

Flush the cooling system and sterndrive to remove build-up of salt, sediment and rust. Flushing requires using a muff style flushing kit that clamps onto the water intake. Ensure the water supply is turned on when the engine is running, or damage will be caused to the water pump and impeller. Start and run the engine for a few minutes to remove the salt crystals.

Drain & Protect

Drain down the fresh water from your engine block and manifolds, circulation water pump, pipes and coolers. Trapped frozen water will expand and crack your engine block and exhaust manifolds. Consult your engine manual for the location of drain plugs. These are usually mounted on the block, manifolds and water pump.

The engine should then be filled with marine antifreeze. There are several methods to complete this (consult your manual), one method uses the muffs to draw the antifreeze mix from a bucket, and it’s then pumped around the system by the engine’s cooling system. Another method is to remove the thermostat housing and pour the antifreeze directly into the engine with a funnel. Some rubber impellers are affected by antifreeze, it may be necessary to remove the impeller from the pump housing if it will remain immersed in the antifreeze.

Engine Fogging

During winter layup, untreated cylinder walls and piston rings will rust, leading to lower performance and shortening engine life. In severe cases, the parts rust can solid, seizing so it will no longer turn. When that happens, the only remedy to this is to disassemble the marine engine, or even replace it with a new long block. Preventing the rust involves a simple technique known as fogging, the coating the cylinder walls and external components with a sticky preservative oil, that won't easily slide off an engine's polished surfaces.

Fogging of the cylinders requires removal of the spark plugs and rotation of the engine to the correct position for fogging.

Fogging oil is available in aerosol cans for easy application. Refer to your Maintenance and Procedures Manual for specifics on this procedure.

Fuel Treatment

Petrol’s life span is finite. Left untreated for several months over the winter, it breaks down into gum and varnish, that can completely clog carburettors and fuel injectors. This will make the engine hard to start, if it will start at all. If the condition is serious, a complete rebuild of the carburettor or cleaning of fuel injectors will be necessary. To avoid these problems, the petrol must be treated with a stabilizer additive to prevent the deterioration. The amount of stabilizer required depends on two variables: the length of time the fuel is to be protected and the quantity of fuel left in the tank.

With the stabilizer added to the tank run the engine for 10-15 minutes to ensure the additive reaches your fuel lines and carb.

Oil & Filters

It is advisable to complete oil and filter changes at the end of the season, to prevent the corrosive contaminants acting on components over the long winter.