How to Winterize the MerCruiser 4.3L V6

by Jared Curtis
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propeller image by Gonçalo Carreira from

You must winterize your MerCruiser 4.3L V6 before storing it. The engine sucks water up from the lake through the impeller to cool the engine. This water does not automatically drain out of the engine. Because water expands when it freezes, it's imperative to drain the water from the engine. The carburetor also needs special attention. To reduce the risk of costly repairs, winterize your boat properly.

Step 1

Open the fuel tank cap and add the appropriate amount of fuel stabilizer into the fuel tank. Refer to the label on the bottle for the proper amount.

Step 2

Remove the boat drain plug with an open-end wrench. It is located at the bottom-rear of the boat.

Step 3

Open the engine compartment and remove the nut holding the spark arrestor on the carburetor using an open end wrench. The spark arrestor is a round, metal air filter.

Step 4

Attach a garden hose to the motor flush tool and place it over the vents on the out drive. Turn the water supply on and allow the air bubbles to work out of the hose before starting the engine.

Step 5

Start the engine and allow it to run for five minutes.

Step 6

Spray fogging oil in and around the carburetor until the engine dies out. This will keep the carburetor clean during the winter.

Step 7

Turn off the water supply and remove the motor flush tool from the out drive.

Step 8

Remove the drain plugs on the bottom of the engine block using an open-end wrench. Refer to your owner's manual for drain plug location, as it varies depending on the year of manufacture. Allow the water to drain from the block completely. Reinstall the drain plugs and tighten them using a wrench.

Step 9

Lower the out drive as far to the ground as possible without hitting it by pressing the button on the throttle assembly. This will keep the gears in the out drive lubricated throughout the winter.

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