Fogging is a crucial step in preparing your outboard for storage. This protective oil coating prevents internal rust and corrosion during months of non-use—the kind of damage that can cause stuck rings, scored cylinders, and poor compression.
It takes just a few minutes but provides significant protection.
Table of Contents
- What Fogging Does
- When to Fog Your Engine
- Fogging Products
- How to Fog a Carbureted Engine
- How to Fog a Fuel-Injected Engine
- FAQ
What Fogging Does
During storage, several factors threaten your engine's internal components:
Moisture:
- Humidity in the air
- Condensation from temperature changes
- Residual combustion moisture
Corrosion targets:
- Cylinder walls
- Piston rings
- Valve seats and stems (4-stroke)
- Combustion chamber surfaces
- Reed valves (2-stroke)
Fogging oil creates a protective film that:
- Clings to metal surfaces
- Displaces moisture
- Resists rust formation
- Lubricates during initial startup
Without this protection, rust can form on cylinder walls in as little as a few weeks in humid conditions.
When to Fog Your Engine
Definitely Fog
- Winter storage (any duration)
- Any storage exceeding 30 days
- Engines used in humid climates
- Engines stored near water
May Skip Fogging
- Very short storage (less than 2 weeks)
- Engines stored in climate-controlled environments
- If you'll run the engine at least monthly
Spring Expectation
When you start a properly fogged engine:
- Expect some smoke initially
- The fogging oil burns off quickly
- Engine should smooth out within 1-2 minutes
- This is completely normal
Fogging Products
Recommended Fogging Oils
| Product | Type | Notes |
|---|---|---|
| Mercury Fogging Oil | Spray | OEM quality |
| Yamaha Fogging Oil | Spray | Designed for Yamaha engines |
| CRC Fogging Oil | Spray | Widely available |
| Sea Foam Spray | Spray | Cleans and protects |
| Engine Fogging Oil (generic) | Spray | Various brands available |
All quality fogging oils work similarly—choose based on availability and price.
What Makes Fogging Oil Special
Fogging oil differs from regular motor oil:
- Higher viscosity when cold - clings to surfaces
- Better moisture displacement - pushes water away
- Longer-lasting film - stays in place for months
- Designed to burn cleanly - minimal residue on startup
Don't substitute regular motor oil—it doesn't provide the same protection.
How to Fog a Carbureted Engine
This is the most common method for carbureted outboards:
What You Need
- Fogging oil spray
- Garden hose with flush muffs (or ear muffs)
- Water supply
- Eye protection
Step-by-Step Procedure
Step 1: Set Up Cooling Water
Connect flush muffs or flush adapter. Turn on water and verify flow.
Step 2: Start and Warm Engine
Start the engine and let it reach operating temperature. This ensures the fogging oil reaches all internal surfaces properly.
Step 3: Increase to Fast Idle
Set throttle to fast idle (about 1500 RPM). This draws more air and oil through the engine.
Step 4: Spray Fogging Oil
- Remove the engine cover
- Locate the carburetor air intake
- Spray fogging oil directly into the carburetor throat
- Use short bursts, 2-3 seconds each
- Engine will smoke—this is normal and desired
- Continue until engine smokes heavily
Step 5: Stall the Engine (Optional)
Some technicians recommend spraying enough fogging oil to stall the engine:
- This ensures cylinders are well-coated
- Creates maximum internal protection
- If engine stalls, don't restart—leave it fogged
Step 6: Shut Down
If the engine didn't stall, shut it off with the key. Turn off water supply.
Multi-Carburetor Engines
For engines with multiple carburetors:
- Spray into each carburetor individually
- Or spray into the common intake manifold
- Ensure all cylinders receive protection
How to Fog a Fuel-Injected Engine
Fuel-injected engines require a different approach since you can't spray into a carburetor:
Method 1: Through Spark Plug Holes
Step 1: Remove Spark Plugs
Remove all spark plugs from the engine.
Step 2: Spray Into Cylinders
- Insert the fogging oil spray straw into each spark plug hole
- Give each cylinder 2-3 second burst
- Rotate to all cylinders
Step 3: Distribute the Oil
- Disconnect the ignition (kill switch wire or fuse)
- With spark plugs out, crank the engine briefly (1-2 seconds)
- This distributes the oil on cylinder walls
Step 4: Reinstall Spark Plugs
Install plugs but don't fully tighten if you want easy removal in spring. Or fully tighten—your choice.
Method 2: Through Throttle Body
Some fuel-injected engines allow spraying into the throttle body:
- Remove air intake/silencer
- With engine running, spray into throttle body
- Similar to carbureted procedure
- Check your engine's service manual
Method 3: Fogging Fuel Additive
Some products add to fuel and fog through the fuel system:
- Add product to fuel tank
- Run engine to circulate
- Shut down—fogging occurs as engine cools
This method is less direct but works for some applications.
Brand-Specific Recommendations
Yamaha
Yamaha outboards recommend their branded fogging oil. For 4-strokes, fog after the final oil change before storage.
Mercury
Mercury outboards recommends Mercury fogging oil. OptiMax and Verado have specific procedures—consult your manual.
Johnson/Evinrude
Johnson/Evinrude 2-strokes fog well through the carburetor. E-TEC models have an automatic storage mode that fogs the engine—check your procedures.
Honda and Suzuki
Honda and Suzuki 4-strokes should be fogged through spark plug holes or throttle body as applicable to your model.
Common Mistakes
Not enough fogging oil:
- Don't be shy with the spray
- Heavy smoke means good coverage
- Better too much than too little
Engine too cold:
- Warm engine first
- Cold metal doesn't coat as well
- Oil distributes better on warm surfaces
Skipping cylinders:
- Ensure all cylinders are treated
- On V6 engines, reach both banks
Forgetting to fog after flushing:
- If you flush, then forget to fog
- Cylinders are clean but unprotected
- Always fog as the final step
Post-Fogging Steps
After fogging, complete your storage preparation:
- Fuel system already treated (before fogging)
- Lower unit oil changed
- Battery removed or on maintainer
- Cover installed
The fogging is one part of complete storage protection.
FAQ
Can I use WD-40 instead of fogging oil?
Not recommended. WD-40 is a water displacer, not a storage protectant. It doesn't provide long-term protection like fogging oil.
How long does fogging protection last?
Properly fogged engines are protected for 6-12 months in typical storage conditions. Very humid or salt air environments may need more frequent attention.
Will fogging oil damage my engine or catalytic system?
No. Fogging oil is designed to burn cleanly. You'll see smoke on startup, but it won't cause lasting problems.
I forgot to fog. Can I do it later without running the engine?
Yes, use the spark plug hole method. Remove plugs, spray into each cylinder, rotate engine by hand, reinstall plugs.
Should I fog a new engine before first storage?
Yes. New engines have no special protection—treat them the same as any engine before storage.
Bottom Line
Fogging takes just a few minutes and provides crucial protection against internal rust during storage. For carbureted engines, spray into the carburetor while running until heavy smoke appears. For fuel-injected engines, spray through the spark plug holes. Use quality fogging oil—not substitutes—and don't be stingy with application. Combined with proper fuel treatment and oil changes, fogging helps ensure your engine starts easily and runs well next season.
