Stingray Boat

IMPORTANT: MerCruiser strongly recommends that winterizing (laying-up) services be performed by an authorized MerCruiser Dealer. Damage caused by freezing is not covered by the MerCruiser Limited Warranty.

Winterizing: A Most Important Job
Winterizing a marine engine is the single most important maintenance duty a boater can perform. If it's done right, very little work needs to be done in preparing a boat for sea the following Spring. More to the point, winterizing greatly extends the life of the power train by protecting all of its varied components from the ravages of corrosion, freezing and dormancy.

Without fogging the cylinders with a protective coating, severe rust occurs. Without flushing the cooling system, salt crystals corrode cooling passages all winter long. If you neglect to drain the gear oil case, trapped water can freeze, expand and destroy the expensive housing.

To help you prepare for winter storage, here's a guide for the winterizing of sterndrives and inboards. Your biggest expense will be for spark plugs and essential fluids such as engine oil, gear oil, fogging oil and antifreeze. The cost of those necessities is money well spent, especially when measured against what it would cost to repair the damage if you were to short change the winter lay-up procedure.

Actually, your biggest investment will be your time. Depending on how comfortable you are with tools, and on whether you have a twin- or single-engine installation, figure on spending anywhere from three to six hours to get the job done right.

To prepare for winter or off season, here is a list of suggestions to keep your boat in top condition:

  • Clean your boat and apply a thin coat of rust inhibitor on the metal hardware and on your steering and control cables.
  • Drain the fluid from your engine block and manifolds, water pumps, and coolers. Frozen water will expand and crack your engine. Consult your engine manual for the location of drain plugs.
  • Stabilize gasoline with additives. Run engine for approximately 15 minutes to ensure that the additives reach the gasoline in your fuel lines.
  • Replace water separating fuel filter.
  • Change engine oil and oil filter.
  • Inspect belts and hoses.
  • Inspect and lubricate steering and trim.
  • Inspect shift/ throttle cables.
  • Fill block, manifold, and circulating pump with propylene glycol antifreeze.
  • Drain and fill sterndrive gear case.
  • Grease sterndrive gimbal bearing and engine coupler.
  • Test run engine and fog it.
  • Remove battery and store in safe, dry place. Check fluid levels.


Battery electrolyte can cause severe eye damage and burns to the skin. Wear goggles, rubber gloves and a protective apron when working with battery. If spillage occurs, immediately wash area with a solution of baking soda and water.

  • Remove interior cushions and jumpseats and store in a cool, dry place. Otherwise, place cushions on end to allow sufficient ventilation.
  • Drain porta potti and fresh water system. Add freshwater antifreeze to water tank and porta potti. Pump antifreeze into the supply lines using the faucets and transom shower.


DO NOT use automotive type radiator antifreeze under any circumstances. It is poisonous. Most fresh water antifreeze protects the system to -50 F and adds color to the water to indicate its presence. Although this type of antifreeze is nontoxic, DO NOT drink the solution. The system must be thoroughly drained and flushed to remove all traces of the color of the antifreeze when the boat is recommissioned.

  • Store boat in a garage or other facility if available. If not, cover the boat with a mooring cover after the interior has been allowed to dry out. The canvas will breathe and allow for sufficient ventilation of the interiors. Moisture and poor air circulation are the main reasons for rot and mildew. This can occur at any time of the year.
  • If your boat is to be stored on a trailer, you should:
    • Block the trailer wheels so the tires are off the ground. This reduces tire deterioration.
    • Loosen tie-down straps to reduce stress on the hull.

Hand Removable Drain Plugs for Easy Winterization
When the time comes to put your boat into hibernation for the winter, you won't need any tools to remove the color-coded plastic drain plugs on both the engine block and the manifolds. The drain plugs are common to all drain plug holes. The sea water pump (on models so equipped) and engine circulating water pump are the only drains requiring tools to winterize. The sea water pump hose must be removed to eliminate any remaining water.

Raw-Water Cooling
Just before fogging the power plant, backwash the cooling system and lower unit of a sterndrive to get rid of salt, sediment and rust flakes. Flushing requires utilizing an ear muff style flushing kit that clamps onto the water intake. Depending on your locale, it may be a good idea to remove the thermostat housing and propylene glycol antifreeze into the cooling system to prevent miniscule ice pockets from forming and cracking the block.

Drain and Fill the Gearcase
With a sterndrive, the gearcase should be drained and refilled after every 100 hours of running time or, at the very minimum, every fall during normally scheduled lay-up. Otherwise corrosion will attack the gear set and bearings. Even worse than rusty gears and bearing races is water trapped inside the lower unit, which can freeze and damage casting.

Steering and Shifting
If the steering cable has grease fittings, lubricate them with grease from a hand operated grease gun while the steering cable is fully retracted into the cable housing. Retract the cable by having someone turn the steering wheel while watching the cable. Lubricate all steering system and throttle/shift system pivot points with SAE 30W motor oil.

Stabilizing the Gasoline
Gasoline's life span is finite. Left untreated for several months over the winter, it deteriorates into gum and varnish that can completely clog carburetor passages or fuel injectors. When that happens an engine is hard to start, if it will start at all. If the condition is serious, a complete rebuild of the carburetor or cleaning of fuel injectors becomes necessary. To avoid that kind of grief, the fuel must be treated with an additive called a stabilizer. The amount of stabilizer required depends on two variables: the length of time the fuel is to be protected and the number of gallons of gasoline in the tank.

Fogging Engine
During extended periods of lay-up (winter), unprotected cylinder walls and piston rings will rust, thereby shortening engine life. In severe cases, the parts rust solid, locking-up the engine so that it won't even turn over. When that happens, the only possible fix is to disassemble the power plant.

Preventing rust involves a simple technique known as fogging, or coating the cylinder walls with a sticky preservative oil that won't easily slide off an engine's polished surfaces. Fogging oil is available in aerosol cans or in straight liquid form by the quart. Refer to the Maintenance and Procedures Manual for specifics on this procedure.

Cosmetic Protection
Sometimes saltwater spray penetrates the engine room through the air-intake ports. If you see salt residue on the power plant, wipe it off. If the engine is really grimy, coat the affected surfaces with engine-cleaning solvent. Give it time to work, then wipe it off.

Hose down the drive unit to wash away any dirt and salt spray that may have accumulated there. If sand has scoured paint off the unit, wash the surface in soap and water, scrub with a bristle brush, then rinse. Prime, then paint exposed metal on the drive leg to protect it from corrosion.

A word of caution: When touching-up outdrive surfaces with a paint can, it's good practice to mask off the sacrificial anodes so over-spraying doesn't insulate these important components from electrolytic activity and thereby render them useless as corrosion inhibitors.

Fighting Corrosion
Inspect the sacrificial anodes located on the outdrive. Over the season, they have been attacked by galvanic action and eaten away little by little. If any anode is less than half its original size, replace it. Regardless of whether or not the anode needs replacing, remove it and make sure there is good metal-to-metal contact between the anode and the housing it protects. Otherwise, it's worthless. Before replacing it, coat the bolts with anticorrosion lubricant. This stops in-place corrosion, which if ignored, could make them nearly impossible to remove later. Remember, unchecked galvanic action can severely damage or even eat away aluminum gear housing.

boat with cover Storing a Boat on a Trailer
If a boat winters on its trailer, leave the drain plug out and cant the bow higher than the stern so rainwater does not accumulate in the bilge where substantial weight could snap the trailer's axle. Sterndrives should be stored in the down position to prevent strain on the exhaust elbows and universal joint bellows.

Note: This is also a good time to replace wheel bearings and touch up trailer paint.

The majority of the information listed on this page is derived from Winterization Tips from MerCruiser, P/N 90-854200-97. For additional information from MerCruiser, visit their website.


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