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Winter storage: Correct preservation for engine and drive

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Proper machine and drive maintenance is essential for a carefree season on the water. Here are the most important tips for doing it yourself

Boat engines, regardless of whether they are gasoline or diesel, will not break down, they say, they break down. This is why professional conservation is particularly important for the winter months to protect them from their declared enemies, rust and frost. The fundamental decision of every owner: do it yourself or order it from a specialist? During the warranty period it would be a mistake not to use the services of an authorized service company. After that, many like to lend a hand themselves, and a lot can indeed be done by laypeople, provided that the work processes are followed correctly. On the one hand, the operating instructions or a corresponding manual from the accessories trade must be consulted; on the other hand, we provide the most important information below on what self-makers should consider when preserving the engine and the various systems and components.

It is often worthwhile to have trained mechanics do the work.

Oil change

The engine oil, the oil filter and the oil in the reverse gear must be changed. This requires a suction pump (permanently installed in larger diesel engines) with a suitable probe and filter tensioner. See article on winterizing

Fuel systems

First you empty the water separator in a key and leave the drain plugs open until there is no more water, just fuel. The filters and filter inserts are then best replaced, with diesel engines being vented afterwards according to the manufacturer's instructions. Only then start the engine and check that everything is tight again.
An effective protection against corrosion in the fuel system are fuel additives, which fight both water deposits and bacteria and thus prevent corrosion and possible damage to the engine. The accessory trade or specialist workshops offer additives only for diesel or only for gasoline engines, and some that are suitable for all engines. Such additives (find out which ones are best) are filled into the tank before the winter work starts, and the engine is left running so that the additives can do their preserving work in the engine.

Oil change on a Mercruiser with a portable electric pump


Check the V-belt regularly for sufficient tension, but especially in spring this step should not be forgotten. To check, you press the middle of the V-belt, which should give about 10 mm. If it is more, it must be retightened. The manual explains which steps and tools are required for this. If the belt shows signs of wear or is even damaged, get rid of it, because with a defective belt you run the risk of insufficient charging of the battery by the alternator, consequential damage to the seawater pump of the cooling system, or stiff steering because the servo pump fails.

Cooling system

Work on the cooling system is best carried out when the boat is already on land. Built-in gasoline engines with so-called single-circuit cooling, consisting of a water filter, pump, gearbox, heat exchanger and exhaust system, must be thoroughly rinsed with fresh water. Either you let the engine run with the flushing connection or pull off the cooling water or suction hose on the sea filter or bottom valve and connect it to a fresh water connection via a garden hose. Make sure that there is always enough water running and allow the engine to warm up for about 15 minutes until the thermostat opens. Then drain the entire cooling system according to the instructions of the engine manufacturer. Caution: Drainage taps and stoppers can be contaminated, so watch whether the water is draining off.

Equipment for flushing a cooling water system with corrosion protection

You can then treat the system with a mixture of water and antifreeze or preservative or a mixture of water and preservative oil, as follows: Suck in this mixture at idle speed through the cooling water pump from a mixing container or bucket and run it completely through the cooling system. However, this must be done as soon as possible after draining, because the thermostat must be open so that this mixture can flow through the entire cooling system. Anyone who has decided on a water-oil mixture has to drain it again because it is not frost-proof. However, the mixture of oil and water is not frost-proof. You are better off with a mixture of water and glycol, because it can and should overwinter in the cooling circuit, provided that it is frost-proof down to at least -25 ° C. Anyone who has to supply a dual-circuit-cooled motor must also take care of the internal circuit, which is filled with coolant. A frost protection spindle is used to check whether the liquid offers sufficient frost protection. If not, some of the coolant must be drained and replaced with antifreeze. In this case, the engine must then run for a few minutes (then check the antifreeze again). Do not forget to also inspect the impeller, for which the cover of the water pump must be unscrewed. Either pull out the impeller with two screwdrivers or special water pump pliers, rinse with fresh water and check for damage. It is best to install the pump wheel with new seals in the spring and store it in a dry place until then. The sieve in the seawater filter should also be removed and cleaned. If the impeller pump is in the sterndrive, a trained mechanic should be consulted for this work.

Air filter

In gasoline engines, air filters consist of wire meshes. Modern diesel engines, on the other hand, lack the air due to paper or foam filters. Paper filters are always changed. Wire and foam filters, on the other hand, are cleaned with white spirit and blown out with compressed air.

Piston and cylinder

To protect these important engine parts from corrosion, the air filter is removed and a protective oil such as WD-40 is sprayed into the intake line or the carburetor while the engine is running. Because the engine should stop running after this, it is advisable to carry out this step at the same time as servicing the cooling system.

Spraying of mechanical parts with preservatives

Ignition system

For winter storage, the ignition cable, distributor and distributor cap are wiped clean and dry and then sprayed inside and out with a contact spray. The latter also applies to the plugs of modern, electronically controlled motors. The replacement of wearing parts is best postponed to the wintering.


Visually check the fuel lines for kinks and chafing and for leaks. Clamps and connections must be checked for tight fit and corrosion and tightened if necessary. Be careful not to over-tighten the set screw. Corroded or over-tightened clamps are best replaced with new ones made of stainless steel.


Obviously, work on the sterndrive can only be carried out on land. The used oil is drained into a sufficiently large collecting pan and replaced with fresh one. If the drained used oil is white and milky, this means that it contains water, if the color is silvery, this indicates mechanical damage to the sterndrive. Both are cases for a trained mechanic.
The easiest way to add fresh oil is through the drain hole. With an oil tube or special pump you push it into the gearbox until it comes out of the control opening or the dipstick is between minimum and maximum. Then the screw plugs with new seals are screwed in first at the top and then at the bottom. don't forget: grease nipples and moving parts of the steering should also be lubricated according to the service manual. Information on the lubrication points and the specific grease can be found in the operating instructions.
Also inspect the bellows, the water intake hose, the electric cables, the power trim cylinder and the hydraulic hoses for damage and wear. A leaky bellows (for example on the drive shaft) can penetrate the drive, which usually leads to major damage.

Removing a Mercruiser sterndrive for service and repair requires professional knowledge.

Propeller and shaft

Propeller must be down so that the shaft can be lubricated with waterproof grease. If the propeller is also made of stainless steel, store it in a safe place to prevent possible theft. Have a specialist repair damaged or bent propellers or, even better, replace them. In boats with a shaft system, the play in the stern tube and on the shaft bracket is also checked. Worn out bushings and bearings should be replaced immediately, shaft seals checked and serviced. In the case of the latter, a distinction is now made between the long-serving stuffing boxes and the newer shaft seals with slide ring or rubber seal. With conventional stuffing boxes, string, grease or oil and the seat of the clamping nut must be inspected. In the case of water-lubricated radial-lip shaft seals, you should check the lips for wear.


Water-cooled exhaust systems in engines with shaft systems usually have water collectors and / or silencers that have to be drained. The drainage screws can be found at the lowest point of the collector or damper. Motors that are installed below the waterline are equipped by the shipyards with a vacuum valve, which should be removed and carefully cleaned.

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