Winterize a 4-Stroke Yamaha Outboard: Complete Checklist + Pro Tips

If your boat will sit 60–90+ days, winterizing a 4-stroke Yamaha prevents corrosion, varnish, and freeze damage – so spring startup is turn-key. Use this fast checklist (with model-safe notes for EFI vs. carb), then grab the exact Yamaha kits you need.

What you’ll need to winterize a 4-stroke Yamaha outboard

To winterize a 4-stroke outboard, stabilize the fuel, flush & drain cooling passages, change engine oil/filter and lower-unit lube, protect cylinders (fogging or storage oil), grease pivots, treat for corrosion, and store the battery indoors.

• Fuel stabilizer (ethanol-safe)
• Yamalube 4M oil + Yamaha oil filter & crush washer (model-specific kit)
• Lower-unit gear lube + pump & drain gaskets
• Fogging/storage oil (see EFI note below)
• Marine grease, corrosion inhibitor, rags
• Motor flusher (“earmuffs”) / hose, drain pan, basic hand tools
• Battery terminal protector & cleaner

Step-by-step:

1) Stabilize fuel (before you do anything else).

Add stabilizer to fresh fuel; run 10–15 min so treated fuel reaches rails/injectors and VST. Fill the tank to reduce condensation (leave expansion room).

2) Flush & drain cooling passages.

On hose port or earmuffs, flush 5–10 min. Tilt fully up, then down to shed trapped water (repeat once). Don’t run on the hose port if your model forbids it – use earmuffs for any engine-on steps.

3) Change engine oil & filter.

Warm the engine, drain, replace crush washer, install OEM filter, fill to spec, run briefly, and re-check dipstick. (Fresh oil sits all winter – no acids.)

4) Change lower-unit gear lube.

Remove bottom plug first, then top vent. Inspect for milky oil (water) or metal. Refill from the bottom up until it exits the vent; install new gaskets; torque.

5) Protect cylinders (fogging/storage oil).

• Carb models: With engine running on earmuffs, spray fogging oil into each carb/air intake until the engine bogs/stalls.
• EFI models: Don’t flood the intake. Disable ignition, remove spark plugs, spray storage oil into each cylinder, and bump the starter a few seconds to distribute. Refit plugs (torque to spec).
  

(Goal: leave a protective film on cylinder walls/rings.)

6) Grease & protect.

Pull the prop, remove fishing line, coat prop shaft lightly with marine grease; reinstall with fresh cotter. Grease steering/tilt pivots. Spray corrosion inhibitor on powerhead & exposed fasteners (avoid belts, sensors, air intakes).

7) Anodes & thermostats quick check.

Replace anodes at ~50% wear; ensure bare metal contact (no paint). If thermostats were sticking/cool-running, plan to replace during this service.

8) Battery & storage.

Rinse/dry the cowling and midsection, disconnect battery, clean and protect terminals, and store the battery cool/dry and off concrete. Leave the motor vertical so water can’t sit in the exhaust passages.

Flush Your Engine

You'll need:

• Motor flusher
• Garden hose
• Water supply

It's important to thoroughly flush your outboard engine to remove any salt build-up if you are a saltwater boater or general mud and grime if you are a freshwater boater. Not removing this debris can cause or contribute to corrosion in the engine. Salt crystals in the lower unit can cause a lot of damage if you're a saltwater boater.

Flushing Your Outboard with the Engine Running

To flush your Yamaha outboard with the engine running, you will use a motor flusher (earmuff style flushers are the most common). Screw your garden hose onto the motor flusher, then slide the motor flusher over the engine's water intakes. You must be sure that the earmuffs are completely covering the water intakes. Using this flushing method, you will turn on the engine. But first, ensure that you have a good water supply and that water is coming out on both sides of the earmuffs.

Flushing Your Outboard with the Engine Not Running

If your outboard has a hose adapter, screw the hose into the port, turn on the water and let the water run for about 5 minutes.

**Warning**

Do not run the engine when flushing while using a hose port. This method is solely designed for flushing while your engine is entirely off.

Final Motor Flushing Steps

Remove the cowling cover and look for any salt or grime build-up that may have settled outside any engine components. If you spot any build-up, rinse it away.

Finally, tilt the engine all the way up, then trim it all the way down to ensure every drop of water drains from the engine.

Stabilize Your Fuel System

You'll need:

• Fuel stabilizer suitable for long-term storage
• Motor flusher
• Garden hose
• Water supply

Because it is so common, many of us use ethanol-enriched gasoline; we recommend using a fuel stabilizer all the time.

Additionally, using a fuel stabilizer like Yamaha Fuel Stabilizer and Conditioner Plus is vital when your boat will be sitting unused for more than two or three months.

Add the amount of fuel stabilizer directed on the product's packing to your fuel—for instance, 1 ounce of Yamaha Fuel Stabilizer and Conditioner Plus for every gallon of gasoline, assuming the engine will be stored for more than two months. If you are storing the engine for two months or less, the suggested ratio from Yamaha is 1 ounce of stabilizer for every 3 gallons of gasoline.

Run the engine with stabilized fuel for 10-15 minutes to thoroughly circulate the stabilized fuel throughout your fuel system. If your boat is out of the water, follow the Flush Your Outboard with the engine running procedures detailed above.

Fogging Your Yamaha Outboard Motor

You'll need:

• Fogging oil
• Crescent wrench
• Replacement spark plugs
• Motor flusher
• Garden hose
• Water supply

Yamalube fogging oil is a wax-based oil that coats the engine and prevents corrosion. As you work through this process, you will soon understand why this process is called fogging the engine, as there will be plenty of white smoke.

Since you will not be in the water while performing this task, you will need to use a motor flusher to keep the engine cool while you complete the fogging process. Follow the "Flush Your Outboard with the Engine Running" procedures detailed above.

If applicable, remove your engine's air cleaner to get to the carburetors or cylinder air intakes.

Rev the engine to a bit above idle, and with the engine running, spray the fogging oil into the carburetor(s) or air intake of each cylinder.

Continuously spray fogging oil into your engine's carburetors or cylinder air intakes until the engine stalls. Be sure to spray a coating of fogging oil into each cylinder or carburetor. However, don't spray too much oil at once and kill the engine immediately, but after a continuous spray, the engine will eventually stall. This is precisely what you want, and the ultimate stalling indicates that the engine is thoroughly covered with fogging oil.

Next, use your crescent wrench to remove the spark plugs and spray fogging oil into each cylinder. Turn the flywheel to move the cylinders allowing you to coat the entire cylinder wall. Rather than turning the flywheel to move the cylinders, you can also simply start the engine for just a few seconds to allow the fogging oil to coat the cylinder walls–repeat this process a couple of times for good measure. Replace old spark plugs with new spark plugs so that you are ready to go in the spring.

Change Lower Unit Oil

You'll need:

• Sufficient quantity of lower unit oil/gear lube oil
• Gear lube/oil pump (for getting oil back into the lower unit)
• Two new drain screw gaskets
• Drain pan
• Large flat head screwdriver
• A few rags

We strongly recommend changing your Yamaha gear lube before storage to ensure no water is in the lower unit's oil. Any water in the oil could freeze, expand, and crack your lower unit. Also, changing lower unit oil means one less thing to do at the beginning of next season.

First, you'll need to know how much lower unit oil/gear lube you need to have on hand. Check your owner's manual for the proper amounts.

Locate the lower and upper lower unit oil drain holes. With your drain pan in position, first, remove the lower drain screw. The oil will start to drip out into the drain pan.

Next, remove the upper drain screw—oil will drain out quickly. Allow the oil to drain completely.

You must pay close attention to your lower unit's oil. If the oil is a milky color, there is water in the lower unit, and you will have significant problems down the road. If this is the case, go directly to your marine mechanic to diagnose the problem and hopefully fix the issue before it causes more damage.

With the oil completely drained, screw in your pump fitting and attach the pump. Remove the cap of your bottle of lower unit oil and screw the pump onto the bottle.

Pump until oil begins flowing out of the upper drain hole.

Install a new lower unit drain gasket onto your upper screw plug. Insert the upper screw plug, hand tighten, then tighten securely with your flathead screwdriver.

Install a new lower unit drain gasket on your lower screw. With the lower screw in your hand, remove the gear oil pump fitting. Quickly insert and tighten the lower screw.

Wipe everything down and properly dispose of your old oil lower unit oil.

**Warning**

There must be no water in your lower unit oil. If there is water in the lower unit oil and your boat is stored in the cold, the water in the oil will freeze and crack your lower unit - an expense no boat owner wants.

Disconnect Your Battery

You'll need:

• Battery terminal cleaner and protector

Disconnect your battery and spray Yamaha Battery Terminal Protector & Cleaner on your battery terminals.

Store your battery in a cool, dry place off of the ground to avoid ongoing exposure to freezing temperatures.

FAQs about winterizing a 4-stroke Yamaha outboard

Do you have to winterize a 4-stroke outboard motor?
Yes – if storing 60–90+ days, winterization prevents corrosion, varnish, and freeze damage.

Should I fog an EFI Yamaha?
Use storage oil via spark-plug holes (don’t soak the throttle body). Carb models can be fogged through the intake.

Why change oil before storage?
Used oil contains acids/contaminants. Fresh oil protects bearings/cam surfaces all winter.

Why change lower-unit lube now?
If water is present, it can freeze and crack the gearcase. Fresh lube prevents that – and it’s one less spring task.

Is filling the tank recommended?
Yes – treat the fuel and fill to minimize condensation; leave expansion headspace.

Where do I spray corrosion inhibitor?
Light coat on the powerhead and external metal – avoid belts, sensors, and air inlets.

Winterizing Yamaha Outboard Engines  – Yamaha Online Parts Has All You Need

Proper Yamaha maintenance requires genuine Yamaha outboard parts and products – Yamaha Online Parts is here to help!