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Fogging coats the inside of your engine with a protective film so rust, sticky piston rings, and gummed-up injectors don’t ruin your first trip next season. If your boat will sit for more than a month or is stored outdoors, near salt air, or anywhere temperatures swing, spending 20 minutes with a can of fogging oil is cheap insurance against repairs that can cost thousands.
What Is “Fogging”?
When we say fogging, we mean spraying a light, sticky oil into the air-intake stream, or directly into each spark-plug hole, so a fine mist “fogs” everything it touches: piston crowns, cylinder walls, valves, injector tips, carb throats, even bare exhaust ports. The micro-film from that spray:
- Blocks oxygen and moisture from raw metal
- Lubricates rings and valve stems during the first dry turns on start-up
- Leaves behind additives that fight varnish and surface pitting
Do You Have to Fog Every Engine?
Not always but skipping it is a gamble. The need for fogging depends on how and where your boat is stored. Use these guidelines to decide if your engine really needs it:
| Storage Situation | Fogging Needed? |
| Kept in a heated shop and engine is started monthly | Usually safe to skip |
| Stored in a garage at 50° F / 10° C or colder, for 5–8 weeks | Recommended |
| Stored on an outdoor rack in a salty or humid climate for any length | Highly recommended |
| Two-stroke with 24:1- 50:1 mix, started every three weeks | Safe to skip |
Think of fogging as a $10 insurance policy, cheap protection compared to the $2,500–$4,500 you could spend on a midsize outboard engine rebuild.
What Happens Inside an Idle Engine
- Moisture condenses on cool metal every time the air warms and cools.
- Salt crystals attract water, creating tiny rust spots.
- Piston rings and valves that sit half-open trap that moisture.
- Surface rust forms within weeks, etching the cross-hatch that seals compression.
- On the first start, the rust scrapes across rings and cylinder walls, so say goodbye to horsepower.
Fogging interrupts the cycle at step 1, stopping moisture before it settles – no condensation, no corrosion, and none of the damage that follows.
When You Can Safely Skip Fogging
- If you’re storing your boat (or engine) for less than a month and keeping it in a climate-controlled, heated area (like a heated garage or shop), fogging usually isn’t necessary. The warm, dry conditions prevent the cycle of condensation that causes corrosion.
- Use keeps internal parts from sitting still long enough to corrode or stick. Taking the boat out and running the engine under load at least once every three weeks also burns off moisture and contaminants that would otherwise linger. In that case, fogging usually isn’t necessary. Just remember, idling on the trailer or in a slip doesn’t count.
- Stroke engines mix oil directly with fuel at ratios like 24:1 or 50:1. That oil/fuel blend continuously coats the internal parts (cylinders, pistons, rings, valves), essentially fogging the engine each time it runs. This built-in protection makes them less prone to rust during short storage, so separate fogging usually isn’t needed. If you’re unsure, fog anyway. It’s faster to do than the research you’re doing now.
How to Fog Your Engine for Storage
Total time: 20 minutes per engine
Supplies:
- Fuel stabilizer
- Fogging oil aerosol
- Spark-plug wrench
- Clean rags
Step 1 – Stabilize the Fuel
Run the boat on treated gasoline for 10 minutes. Fuel stabilizer prevents gas from turning gummy while you work through the rest of the checklist.
Step 2 – Warm the Engine
Attach a water supply (muffs or flush-port) and idle 5 – 10 minutes. Warm metal holds an oil film much better than a cold block.
Step 3 – Remove the Flame Arrestor
Slip off the air filter so you can spray fogging oil directly into the throttle throat.
Step 4 – Fog the Intake
With the engine idling slightly above normal (1,100–1,200 rpm):
- Short Bursts: Spray two-second shots into the throat every few seconds.
- Watch the Exhaust: Dense white smoke or a cough means you’re getting coverage.
- Final Blast: A 5-second spray usually stalls the engine – that’s perfect.
Step 5 – Treat the Cylinders
Remove each spark plug and spray about 1 fl oz (30 ml) of fogging oil or drizzle a capful of clean engine oil into every cylinder.
Step 6 – Rotate the Crank
Disable ignition or fuel (safety first), then spin the starter 2–3 seconds. This spreads the oil evenly on rings and cylinder walls.
Step 7 – Button Up
Reinstall the spark plugs. Many skippers keep the old set in for the smoky spring start, then swap in fresh plugs once the excess oil has burned off.
Variations You’ll Run Into
- Multi-Throttle EFI: Use the factory fog-port or the specified oil-fuel mixture.
- Direct-Injected Two-Strokes: Still benefit from fogging; spray through the throttle while the oil pump continues feeding bearings.
- Built-In Fog-Port Outboards: Snap the aerosol tube on the fitting, hold the trigger, and you’re done.
Added Winterizing Moves That Pair Well with Fogging
- Drain or antifreeze-flush raw-water passages if your region experiences freezing temperatures.
- Change gear-case and crankcase oils to remove water and acids.
- Top up the fuel tank and add stabilizer to curb phase separation.
- Disconnect the batteries and keep them on a smart charger.
- Grease u-joints and splines while the cowl is open.
Fogging is just one spoke in the winterizing wheel, but it’s the quickest and easiest to check off.
Benefits You’ll Notice in Spring
- First-start confidence – no dry bearings screeching awake.
- Smooth idle – rings that slide instead of scrape.
- Clean spark plugs – additives prevent carbon from baking on.
- Longer injector life – coated nozzles resist varnish buildup.
Common Mistakes to Avoid
| Mistake | Why It Matters | Fix |
| Spraying too much oil and cranking immediately | Can hydro-lock a cylinder | Follow the 1 oz guideline |
| Forgetting water flow during warm-up | Impeller scorches in seconds | Hook up muffs before key-on |
| Leaving spark plugs loose | Moisture sneaks back in | Torque to spec |
| Storing with near-empty fuel tank | Condensation pools inside | Fill and stabilize |
Frequently Asked Questions
Does fogging void my warranty?
No. In fact, most OEM manuals recommend fogging for extended storage. Just be sure to use an approved product.
My engine won’t stall during the final spray. Did I under-fog?
Not necessarily. Modern ECU-controlled motors may fight to stay running. As long as you see heavy white smoke, you’ve got enough coverage.
Can I use WD-40 instead?
No. Penetrating oils like WD-40 evaporate. Fogging oils contain tackifiers that leave a clingy film built to last for months, not minutes.
What about diesel inboards?
Diesels rarely need fogging because their heavier oil residue already coats the cylinder walls. However, spraying the intake when you shut down for the season is added insurance.
The Cost of Skipping Fogging
Surface rust that sneaks under a piston ring can seize it in its groove, dropping compression in that cylinder. If a stuck ring scratches the bore, you’re looking at a tear-down and hone at minimum. Full rebuilds on midsize motors start around $2,500, and modern four-strokes can easily climb past $6,000. All to fix damage that a $10 can and 20 minutes of routine care can prevent.
Ready for Stress-Free Launch Day?
Fogging and the broader de-winterizing checklist keep your boat ready for adventure, but even the best-maintained engine can surprise you. That’s why boaters keep a Sea Tow® membership. Membership means unlimited towing in your home area, jump-starts, fuel drops, and a 24/7 direct connection to your local Captain. For Peace of Mind on the Water™, choose the membership that fits your boating style.
Stay safe, protect your engine, and we’ll see you on the water.
Sea Tow Team
Sea Tow has been the premier leader in on-water boating assistance since 1983. We want to share news, press, tips and all things boating.