Defend Against the Elements



While your Yamaha Marine dealer can help you with, or even do, most of your general and preventative maintenance, corrosion mitigation is something you can only do yourself—and time is of the essence.

Regardless of where you boat, corrosion attacks both the inside and the outside of your outboard—every day, all the time. Some forms you can see, some you can’t, and it can take only a short time for the damage to begin. Even those boating in freshwater have corrosion-mitigation duties to attend to. Why, even rainwater can have corrosive effects that can be damaging to your outboard. So, it’s vital to be diligent in your anti-corrosion defense.

Your dealer can help provide the right products to help prevent some forms of corrosion, but their regular and diligent use is strictly up to you. The following are answers to common questions about how to mitigate the presence and damage of corrosion.

Where do I need to concentrate my fight against corrosion?

Corrosion can happen pretty much anywhere on or in your outboard: inside, in your fuel system or in the internal cooling water passages, and on the outside, in various electrical connections and exposed metal components. But don’t worry, you have a lot of allies on your side, and we’re here to help by teaching you where to look and what to look for.

What’s so important about flushing my outboard? I boat exclusively in freshwater; do I still need to?

Your Yamaha outboard is raw-water cooled, meaning it uses the water it’s operating on as cooling water. All water, fresh or salt, contains contaminants that will eventually build up in the cooling passages over time. Additionally, saltwater is naturally corrosive and any remaining in those cooling water passages after use is left there to do its worst, unabated. Saltwater can also experience crystallization when exposed to heat above 170 degrees, which causes deposits to form and potentially restrict cooling water passages. For these reasons, it’s a must that you flush your engine thoroughly with fresh, clean water after every use.

How do I go about flushing my outboard?

Use one of these three basic methods to flush after each trip.

  • Use the built-in flush attachment. This is a great procedure to follow, especially if you can’t remove your boat from the water, or if your outboard has dual water inlets and you don’t have the special adapter. Simply connect a garden hose to the inlet side of your non-running outboard’s built-in flush attachment, turn the spigot on full blast, and let the hose’s water pressure do the work. Let the water run for 15 minutes to ensure it fully circulates through the entire cooling system several times. If your boat’s out of the water, like on a trailer or a lift, the fresh water will also trickle down and adequately clean the water pump and the lower unit’s cooling water passages.
  • The flush muff method. This is the most common and often-used fresh water flushing method. Simply connect a garden hose to clean fresh water on one end and a “flush muff” attachment, which slides around the lower unit to provide water to both sides of the raw water inlet, to the other end. Turn on the water until you see water squirting out the sides of the flush muff, then start your outboard in neutral. Set the outboard to no more than a fast idle (900-RPM max) and allow to run for 15 minutes in neutral. Increase hose water pressure enough to maintain a bit of squirting out from under the flush muffs at all times while the outboard is running. This helps ensure it gets fed enough cooling water.

 Note: Outboards utilizing two cooling water inlets require a special adapter to use this method. Check with your outboard’s manufacturer.

 Note: Increasing engine speed may cause water demand to exceed supply. If you notice the hose becoming flat while the outboard is running using this procedure, increase the water flow and/or decrease the engine RPM.

 Warning: For safety, we suggest you remove the propeller before you begin. Accidental engagement of the outboard into gear with the outboard running will cause an exposed propeller to spin rapidly, possibly resulting in serious injury or death.

  • The flush bag method. This method can be used for a boat on a trailer or when moored. A flush bag, when filled with water, simulates the outboard idling in its normal state but immerses the lower unit in fresh, clean tap water. Simply place the bag around the outboard, attach the hose, and fill the bag. Ensure the water level reaches the height of the outboard’s water pump (about 1” above the lower unit separation seam). Start the engine, and run for 15 minutes in neutral. Leave the hose running during this entire procedure. When complete, stop the outboard, then the hose, and then drain the bag.

 Note: Thoroughly dry the bag before storage.

What is “dry corrosion”? What causes it and what can I do about it?

Dry corrosion occurs in areas not in direct contact with water—exhaust systems, for example. The outside of most exhaust system components is cooled by raw water to prevent overheating. When today’s ethanol-enhanced fuel is burned, it creates by-products known as sulfate salts. These salts are highly corrosive, especially when exposed to very hot temperatures. If the outboard’s cooling water passages are not kept clean by regular flushing (the exhaust area in this example), hot spots can form on the interior of the exhaust components, concentrating the sulfate salts’ corrosive effects. In effect, it’s corrosion from the inside out. That’s why flushing your engine with fresh, clean water for 15 minutes after each trip is a vital part of preventing even dry corrosion. It helps the cooling system run at maximum efficiency by keeping the cooling water passages clean and clear, which helps minimize the heat inside the engine, making it less susceptible to dry corrosion.

How can I fight corrosion on the outside of my outboard?

It’s a good practice to set up a regular schedule and stick to it. There are quick and simple things you should do after every use if you boat in saltwater, and periodically if freshwater is your game. These include visual inspections you should do every time. If you’re unsure about what to do and when, your authorized Yamaha Marine dealer can help.

  1. Rinse it.  Don’t spare the hose when returning from a trip, particularly in saltwater.  Rinse the entire outside of the outboard with clean water.  Give is a once over with some mild soap like Yamalube® Wash & Wax Concentrate and a soft cloth while you’re at it (do not use liquid dish detergent – it can strip off important protectants).  Go ahead and wash the whole boat and trailer.   Wiping it down with a good quality chamois afterward helps keep it all looking sharp.

Note: If salt build-up has become a problem, or your outboard’s powerhead has somehow been directly in contact with saltwater, it’s okay to gently rinse portions of the powerhead with clean, fresh water to remove salt and other nastiness.  Just use a hose on low pressure – not a spray attachment – and don’t rinse around the air intake area.  Rinse out the inside of the cowling, too.  Make absolutely sure both the powerhead and the cowling are completely air-dry before re-installing the cowling.

  1. Spray it.  Liberally spray the entire dry powerhead with a protectant like Yamashield.   It’s a lubricant, a water displacement agent and a corrosion preventative all rolled into one.  A high-quality silicone spray works well here, too.  Spray all external powerhead surfaces and the electrical connections to help keep them corrosion-free, and the rubber cowling sealing gaskets to help keep them supple and effective at sealing out harmful water.
  2. Check it.  Do a quick visual inspection of your boat and your Yamaha outboard(s) every time you use them.  Look for anything out of the ordinary and investigate if need be.

Keep a special eye on:

Anodes:  Anodes intentionally corrode before your outboard does, in order to help protect it.   Better known as “sacrificial anodes,” they are typically dull grey in color.  On Yamaha outboards, they’re usually located on the lower unit just above the prop and on the bottom of the engine bracket.  As corrosion occurs over time, they begin to “dissolve.”  Replace them when they are about 50% gone with only high-quality, factory-recommended replacements.  Don’t be fooled by lesser-quality imitations.  There’s too much at stake here to risk it.  Yamaha sacrificial anodes are made of a blend of high-quality alloys specifically designed to help protect your Yamaha outboard.

Caution: Never paint or cover anodes in any way, as they must be in direct contact with the water in order to perform correctly.  When exposed to the water (especially freshwater), they can become covered with a layer of organic growth (often referred to as “scum”).  This is often so thin you won’t even notice it, but it can prevent an anode from doing its job.  Therefore, during your regular washdown procedure, make sure to take a brush and some soap to the anodes to keep them clean and in direct contact with the water.   This will help keep them working properly.

Propellers:  Even stainless-steel propellers can get corrosion on them.  Although most often attributable to external forces like stray voltage in the water, which is not in any way attributable to the prop itself, it nonetheless detracts from the shiny finish you expect it to have.  If your props do get surface discoloration on them (which often appears as a flat grey or light rusty color), there are simple methods by which to clean and protect them using readily available materials.

Electrical systems:  Not just your outboard’s, but your boat’s.  Look under the console and in the bilge areas for electrical connection blocks.  Also, check the battery terminals.  If corrosion appears on either, Yamalube® Battery Terminal Cleaner & Protector will do the trick.  Spray it on to clean the affected areas (heavily corroded connections will first need to be disconnected and thoroughly cleaned).  When it dries, it leaves a protective waxy film that will help keep corrosion from re-forming.