How to Change an Outboard’s Internal Anodes

Your outboard engine has external sacrificial anodes that need to be changed once or twice a year. But did you know outboards also have internal anodes?

Outboard engine internal anodes

Just like the external anodes or zincs, internal anodes are easy to replace and the job can be done in minutes. Most of the bolts holding internal anodes are accessed using a ratchet with an extension bar and a socket piece of the corresponding size. 

Locating the Internal Anodes

To find the internal zincs, consult the outboard’s owner’s or service manual. Most outboards have three or four internal anodes, although some larger units may have up to 10. The anodes are set into the engine block at various points to interact with the water within the engine’s cooling system. Typically the zincs are at the induction end (near the spark plugs) and toward the exhaust end of the block.

 Yamaha outboard internal anode

 Sierra Mercury magnesium anode

Removing Internal Anodes

The internal anodes are attached to protective caps or covers bolted to the motor. To remove the anodes, take off the bolts holding the covers using a ratchet and socket piece, then pull the cover and anode out from the motor with pliers. Next, unbolt the anode from the cover and clean the cover and bolts. If an anode doesn’t pull free with the pliers, slightly turn the anode bolt using a ratchet to break the anode free. Scrape away any salt deposits from around the anode ports, then shoot compressed air into the cooling system via the anode ports to remove any large salt deposits.

Replacing Internal Anodes

Bolt the new internal anodes into the anode covers, then bolt the covers back onto the engine block. Once the internal zincs have been replaced, flush the cooling system with a salt remover to break down any remaining salt deposits and remove all debris.

Replacing anodes is just a small part of protecting your outboard from corrosion. Watch the video above to learn about more ways to prevent outboard corrosion



Commercial Discounts

Special discounts for companies in the marine industry


Government Sales

Discounts for federal and most state and municipal agencies