Winterizing Yamaha Outboard Motors - Here's How

Winterizing Yamaha Outboards

As fall approaches, it's time for many boaters to begin thinking about how to winterize Yamaha outboard motors before storing their boat for season. Proper storage and winterizing avoid potential engine damage and allows a smooth start to the beginning of the next season.

While there are several things you can do before storing your boat to get a jump on next season, the timing of some tasks is up to a boater's personal preference. However, the following six tasks are either necessary or highly recommended.

  1. Thoroughly flush your Yamaha outboard motor
  2. Stabilize your fuel system
  3. Fog your outboard engine
  4. Change your spark plugs
  5. Change lower unit oil
  6. Disconnect your battery

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.

Start the engine and ensure water is flowing from the telltale. Assure that your engine is not overheating by holding your hand under the telltale water stream. It should not be uncomfortable to hold your hand in the stream of water. If the water is excessively hot, water is not flowing correctly, and you are overheating your engine—turn off the engine, reposition the earmuffs, and start again.

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.


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.


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.

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!

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