Winterizing your Mercury 250 Pro XS is essential for maintaining engine performance and preventing damage caused by cold temperatures and prolonged inactivity. Without proper winterization, your outboard motor is vulnerable to fuel degradation, internal corrosion, and freezing damage, which can lead to costly repairs in the spring.
This guide provides a detailed, step-by-step process to winterize your Mercury 250 Pro XS effectively, ensuring a hassle-free start when boating season returns.
Why Winterization is Important
1. Prevents Engine Damage
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Cold temperatures can cause cracks in engine components if water is left inside.
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The cooling system must be free of moisture to prevent ice expansion damage.
2. Protects the Fuel System
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Ethanol-blended fuel absorbs moisture, leading to phase separation and clogged injectors.
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Old fuel can gum up the carburetor and fuel lines, causing poor performance.
3. Extends the Lifespan of Your Engine
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Lubrication prevents internal corrosion and rust.
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Ensures your outboard starts smoothly in spring without unnecessary repairs.
Tools and Supplies Needed
Before starting, gather the following supplies:
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Fuel stabilizer
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Fogging oil
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Engine flush kit
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Freshwater supply
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SAE 90 lower unit gear oil
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Drain pan
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New fuel filter and oil filter
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Marine-grade engine oil
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Spark plug wrench
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Grease gun with marine grease
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Battery trickle charger
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Clean rags and safety gloves
Step-by-Step Guide to Winterizing Mercury 250 Pro XS
1. Add Fuel Stabilizer
Stabilizing the fuel prevents degradation and protects fuel system components.
Steps:
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Fill the fuel tank at least ¾ full to minimize condensation.
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Add the recommended amount of marine fuel stabilizer based on the fuel capacity.
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Run the engine for 10 minutes to circulate the treated fuel through the system.
2. Flush the Cooling System
Flushing removes salt, dirt, and contaminants that can cause blockages.
Steps:
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Connect a flush hose or earmuffs to the engine’s water intake.
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Start the engine and let it idle for 10-15 minutes to flush the system.
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Ensure a steady water flow from the telltale (pee hole).
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Shut down the engine and remove the flush kit.
3. Apply Fogging Oil
Fogging oil lubricates the engine’s internal parts and prevents corrosion.
Steps:
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Remove the engine cowling to access the air intake.
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Spray fogging oil into the air intake while the engine is running at low RPMs.
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Continue spraying until you see white smoke from the exhaust.
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Turn off the engine and reinstall the cowling.
4. Change Engine Oil and Filter
Old oil contains contaminants that can cause corrosion and wear.
Steps:
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Run the engine for 5 minutes to warm up the oil.
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Remove the oil drain plug and let the oil drain completely into a pan.
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Replace with fresh marine-grade engine oil.
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Install a new oil filter and tighten it securely.
5. Drain and Refill Lower Unit Gear Oil
Water in the gear case can freeze, leading to cracked seals and internal damage.
Steps:
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Position a drain pan under the lower unit.
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Remove the lower drain screw, followed by the upper vent screw.
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Let the old gear oil drain completely.
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Inspect the oil for milky color, which indicates water contamination.
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Refill with fresh SAE 90 marine gear oil using a gear pump.
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Reinstall the drain and vent screws securely.
6. Replace the Fuel Filter
Replacing the fuel filter ensures the engine receives clean fuel during the next season.
Steps:
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Locate the fuel filter inside the engine cowling.
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Remove the old filter and check for debris or water contamination.
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Install a new fuel filter and tighten it securely.
7. Check and Replace Spark Plugs
Worn-out spark plugs cause starting issues and misfires.
Steps:
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Use a spark plug wrench to remove each spark plug.
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Inspect for carbon buildup, wear, or moisture damage.
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Install new spark plugs and tighten them to specifications.
8. Lubricate Moving Parts
Proper lubrication prevents rust and stiffness during storage.
Steps:
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Apply marine grease to the steering linkage, throttle cables, and pivot points.
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Grease the propeller shaft before reinstalling the prop.
9. Remove and Store the Battery
Cold temperatures can drain and damage the battery over time.
Steps:
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Disconnect the negative (-) terminal first, followed by the positive (+) terminal.
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Store the battery in a cool, dry place on a trickle charger.
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Clean the battery terminals and apply anti-corrosion grease.
10. Store the Engine Properly
Storing the Mercury 250 Pro XS correctly protects it from dust, moisture, and temperature fluctuations.
Steps:
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Store the boat in a covered, well-ventilated space.
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Use an engine cover to prevent dust accumulation.
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Tilt the engine downward to allow any remaining water to drain.
Common Winterization Mistakes to Avoid
1. Forgetting to Use Fuel Stabilizer
- Stale fuel clogs the carburetor and fuel injectors, leading to performance issues.
2. Not Draining the Lower Unit
- Water inside the gear case can freeze and cause cracks in the housing.
3. Skipping Fogging Oil
- Internal corrosion can lead to stuck pistons and rings after long storage.
4. Leaving the Battery Connected
- A dead battery in spring can cause starting issues and added expenses.
FAQs About Winterizing Mercury 250 Pro XS
1. How Often Should I Winterize My Outboard?
- Every off-season or when the engine will be idle for more than 30 days.
2. Can I Skip Changing the Oil?
- No. Old oil contains contaminants that cause internal wear.
3. Should I Remove the Propeller?
- Yes. It allows you to inspect the shaft for fishing line or debris.
4. Do I Need a Professional to Winterize My Engine?
- If you’re comfortable with DIY maintenance, you can do it yourself. Otherwise, a marine mechanic can ensure proper winterization.
Taking the time to winterize your Mercury 250 Pro XS ensures optimal performance and longevity. Proper fuel stabilization, lubrication, and storage will prevent costly repairs and make spring startup smooth and effortless.
By following these step-by-step instructions, you can protect your outboard engine from winter damage and enjoy hassle-free boating next season!