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John White
John White, Marine Mechanic
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Experience:  11 years experience working on outboards, inboards, sterndrives & pwcs
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How To Winterize An Outboard Motor?

I have a 150  Optimax... Show More

I have a 150  Optimax outboard motor. How do I winterize it?

Submitted: 7 years ago.
Category: Boat
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replied 7 years ago.

Below is the winterizing procedure from Mercury. Towards the end of the procedure when it tells you to pour engine oil into each spark plug hole it is referring to the optimax 2-stroke oil you put in the oil tank. A turkey baster works well for measuring the amount and getting it into the plug holes without a mess. Do not use fogging oil on an optimax engine.

IMPORTANT: Fuel containing alcohol (ethanol or methanol) can cause a formation of acid during storage that can damage the fuel system. If the fuel being used contains alcohol, Mercury Marine recommends draining as much of the remaining fuel from the fuel tank, remote fuel line and engine system.
The most effective method for storage preparation is to add the recommended amount of Mercury Precision Fuel Stabilizer and Mercury Precision Quickleen products, as described on their respective containers, to the fuel tank before the final operation of the boat prior to storage. Fuel stabilizer helps prevent the formation of varnish and gum in the fuel. Quickleen helps clean and lubricate the fuel injectors.

1. Pour additives into the fuel:
a. Portable Fuel Tank: Pour the required amount of fuel stabilizer into the fuel tank. Close the tank and tip back and forth to mix.
b. Permanently Installed Fuel Tank - Pour the required amount of fuel stabilizer into a separate container. Add approximately one quart of fuel to the container. Mix and pour into the fuel tank.
2. Remove the drain hose from the aft hose fitting (right side of the chamber). Hold the unattached end of the hose over a suitable container.
3. Loosen the filter drain screw (left side of the chamber) and allow contents to drain.
NOTE: If little or no liquid drains from the hose, loosen the red filter to vent the chamber
4. Tighten drain screw and reattach the hose.
5. Remove the drain hose from the forward hose fitting (left side of the chamber). Hold the unattached end of the hose over a suitable container.
6. Loosen the float chamber drain screw (right side of chamber) and allow the contents to drain.
7. Tighten drain screw and reattach the hose.
8. Premix the follow in a container:

  • 8cc (0.3 oz) or 2 teaspoons of Mercury Precision Quickleen lubricant

  • 8cc (0.3 oz) or 2 teaspoons of Mercury Precision Fuel Stabilizer

9. Remove the fuel filter.
10. Pour the mixture into the fuel filter opening.
11. Install the fuel filter.
12. Prime the fuel system.
13. Place the outboard in water or use the flushing attachment for circulating cooling water. Start the engine and run at idle speed for 5 minutes to allow the treated fuel to fill the fuel system.

NOTE: Make sure the fuel system has been prepared for storage.
1. Remove the spark plugs and add approximately 30ml (1oz) of engine oil into each spark plug hole.
2. Rotate the flywheel manually several times to distribute the oil in the cylinders.
3. Re-install spark plugs.


1. Lubricate all outboard components listed in the Inspection and Maintenance


2. Touch up any paint nicks. See your dealer for touch-up paint.

3. Spray Quicksilver Corrosion Guard on external metal surfaces (except corrosion control anodes).


Drain and refill the gear case lubricant (refer to maintenance procedure).


Store outboard in an upright (vertical) position to allow water to drain out of outboard.


If outboard is stored tilted up in freezing temperature, trapped cooling water or

rain water that may have entered the propeller exhaust outlet in the gear case

could freeze and cause damage to the outboard.


1. Follow the battery manufacturers instructions for storage and recharging.

2. Remove the battery from the boat and check water level. Recharge if necessary.

3. Store the battery in a cool, dry place.

4. Periodically check the water level and recharge the battery during storage.

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