How to Fog an Engine for Storage

What fogging does: when an engine sits for months, moisture can form a thin layer of rust on cylinder walls, piston rings and valves. Fogging oil is a sticky storage oil that coats these parts and protects them until spring.

When it applies:

• Storage of a month or more (winter layup, or a long summer break in hot humid climates).
• Carbureted 2-strokes and 4-strokes: classic fogging candidates.
• Fuel-injected (EFI) 4-strokes: most makers still recommend fogging, but often with a specific EFI fogging product and method. Some say to spray through the spark plug holes rather than the intake.
• Direct-injection 2-strokes (for example Mercury OptiMax): Mercury says to skip fogging spray and put a small amount of the specified 2-stroke oil into each cylinder through the plug hole instead.
• Engines with a built-in storage or winterizing mode (some Evinrude E-TEC models): use that mode.
• Storage additive in the fuel: some makers instead have you mix a storage product into a portable tank of fuel and run the engine on it (Mercury's MPI sterndrives use a special fuel-and-oil mix, for example). If your manual says this, it replaces spray fogging.
• PWCs: Yamaha recommends having a technician fog WaveRunners because of their air intake design; Sea-Doo describes a plug-hole method. See the PWC guide.

The rule: the procedure in your owner's manual beats any general guide, including this one. Spraying the wrong product into an EFI intake can foul sensors or the throttle body on some engines.

Order of operations: fogging is usually done near the end of winterization, after fuel has been stabilized and run through the engine, and after the oil change. Fogging while the engine is still warm works best.

• Spraying a regular fogging can into the intake of a fuel-injected engine whose manual calls for an EFI product or the plug-hole method.
• Emptying half a can into the engine. Too much oil fouls plugs and makes the spring start miserable.
• Fogging before the stabilized fuel has been run through, or fogging a cold engine.
• Trying to fog through the built-in flush port. Intake fogging needs the engine running, so use muffs or a flush bag.
• Cranking with the plugs out while the kill-switch clip is still attached and the plug wires are loose.
• Starting the engine again "one last time" after fogging, which burns off the protective coat.
• Leaving a rag in a plug hole or the intake cover off over the winter.

• Your manual does not cover fogging and you have an EFI, direct-injection or supercharged engine
• The engine is under warranty and storage prep must be dealer-performed
• You have a PWC with a complex intake (Yamaha recommends dealer fogging)
• The engine runs badly, overheats or will not restart after fogging
• You notice a fuel smell or leak during the process

• Do not over-fog. More is not better; excess oil can foul plugs and cause hard starting.
• Keep the fogging can warm (room temperature) for a fine, even spray.
• If you boat year-round and never store more than a few weeks, you likely do not need to fog. Check your manual.
• Log the date and method in BoatMend so next spring you know to expect smoke and check plugs.
• Carbureted engine stored two months or more? Mercury's storage advice is to treat the fuel, run the engine about 10 minutes, then shut the fuel valve (or disconnect the line) and let it run until it stops, so the carburetor is not left full of fuel. Some manuals combine this with intake fogging as the engine runs out; follow yours. Some brands also sell a rust-inhibitor storage product to use along with or instead of fogging oil, used only as the manual directs.