When it comes to storing a gasoline engine—whether it’s an inboard, outboard or I/O—for long periods, preserving the fuel and protecting the engine’s internal components from corrosion are the 2 main goals. After you’ve run conditioned and stabilized fuel through the engine, the next step is protecting the engine’s cylinders and other internal spaces where moisture can accumulate and cause rust and corrosion during layup.

It’s important to note that different types (eg., 2-stroke, 4-stroke, EFI, DFI) and brands of engines have different storage requirements. Always check with the manufacturer or your owner’s manual to learn the recommended procedure for your specific make and model of engine. If you’re unsure, you’re better off taking your engine to a qualified marine mechanic or dealer. The procedures outlined below are general recommendations only, and may not be right for your particular engine.

You can also watch a video on the winterizing process here:

Carbureted Engines


If you have an older carbureted engine, you can protect it by spraying fogging oil directly into the carburetor(s) and cylinders. Some mechanics recommend spraying the fogging oil into the air intake while the engine is running at idle or just above idle so the oil-mist can work its way through the carburetor(s), cylinders and exhaust system. If you go this route, you may need to adjust the throttle to keep the engine from stalling out as you introduce the fogging oil. When thick, blue smoke begins billowing out of the exhaust, idle down and keep spraying fogging oil into the air intake until the engine stalls.

Now remove the spark plugs and spray fogging oil into each cylinder via the plug sockets. Replace the spark plugs (make sure you tighten them to spec) and rotate the flywheel to spread the oil over the cylinder walls. You can rotate the flywheel manually or by turning the ignition key. In either case, make sure all the plugs leads are disconnected so the engine will not accidentally fire.

Another method of fogging the engine is to open the carburetor(s) manually and spray fogging oil directly into the carbs while the engine is shut down, then remove the spark plugs and spray fogging oil into each cylinder. (If you need to replace the plugs, wait until spring and after you’ve burned the fogging oil out of the cylinders.)

Re-install the spark plugs and rotate the flywheel manually or by “bumping” the ignition key to distribute oil over the cylinder walls. Again, make sure the spark plug leads are disconnected before you do this so you won’t burn off the oil by starting the engine.

Direct-Injection Engines


With a direct-injection engine, fogging is not recommended (outboard service technicians use a special device for protecting the internal engine components, but it is expensive). However, there are ways to do it yourself, but be sure to consult your owner’s manual or the manufacturer. For example, the owner’s manual for a 2004 200-hp Mercury OptiMax DFI outboard recommends simply removing the spark plugs and introducing 30 milliliters of 2-stroke engine oil directly into each cylinder via the plug sockets.

Once oil has been added to each cylinder, re-install the spark plugs and tighten with a torque wrench, but do not reattach the leads. Manually turn the flywheel several times to distribute oil throughout the cylinders.

Lastly, place a dollop of dialectric grease inside each end cap of the spark plug leads and attach them to the plug terminals.


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