How to Change an Outboard’s External Anodes

Anodes (or zincs) need to be replaced at least once year as part of an outboard’s routine maintenance.

Fortunately, changing the external anodes on an outboard is incredibly easy! Basically if you can hold and turn a wrench, you can replace outboard anodes yourself.

Tools Needed – Replacing Outboard External Anodes

• Open-end wrench
• Ratchet, extension bar and socket pieces

Most of the bolts holding the zincs will be 8mm - 10mm (5/16” - 3/8”), and are easily accessible using a socket piece or open-end wrench. Replace any anode bolts that are corroded, and be careful not to overtighten any bolts or strip the threads.

NOTE: An outboard has both external and internal anodes. The exact location varies from outboard to outboard.

Replacing Transom Bracket Anodes

There will be 2-3 anodes on the mounting bracket that secure the outboard to the transom. Remove the bolt fastenings with either a wrench or ratchet and socket, then remove the anodes and tighten the bolts back in place.

PRO TIP: Trim the engine all the way up to get access to the transom bracket zincs.  

Replacing Side Pocket Anodes

One or two zincs will be located to the bottom and rear of the midsection, just above the anti-ventilation plate. These zincs either bolt on from the side, or are secured by a top-mounted bolt that can be accessed by removing the protective cap in the mid section’s bodywork.

PRO TIP: Use a ratchet extension bar to reach a top-mounted bolt securing a side pocket anode.

Replacing Trim Tab Anodes

The trim tab anode is either secured by a top-mounted or a bottom-mounted bolt. A bottom bolt is straightforward to remove, but a top-mounted bolt has to be accessed by removing the protective cap in the mid section’s bodywork and using a ratchet extension bar.

PRO TIP: The old trim tab zinc might be offset to counter torque steering. Note the position of the old zinc and fit the new one in the same position.

Lower Unit Anodes and Prop Anodes

Some outboards have lower unit anodes in the sides of the gearbox unit, just below the anti-ventilation plate and above the propeller. Anodes may also be found on the propeller shaft or securing the propeller itself. A propeller nut anode is straightforward to replace. However, a prop shaft zinc located on the prop shaft on the opposite side of the propeller must be removed before the old zinc can be replaced.