Sierra 18-6241 Magnesium Anode, Replaces Mercury 31640, MerCruiser Alpha One and R/MR Stern Drives

The Sierra 18-6241 is a magnesium sacrificial anode engineered to protect MerCruiser stern drive components from galvanic corrosion in freshwater use. Magnesium anodes are the correct choice for freshwater boating because magnesium is more electrochemically active than zinc, giving it the sacrificial capacity needed to protect metal components when the boat is not operated in saltwater. The anode corrodes in place of the surrounding drive metal, extending the service life of the gear housing, transom assembly, and related hardware. It is a direct-fit replacement for the OEM Mercury/MerCruiser anode and is manufactured to meet or exceed the specifications of the original equipment part it replaces.

This anode is designed for use on R/MR/Alpha One, Sterndrive and Transom Assembly (1983-90) and prior drives, as well as Alpha One, Gen II (1991 and up) drives. Regular anode inspection and replacement is a routine part of stern drive maintenance and helps prevent costly corrosion damage to the drive unit.

Specifications

• Brand: Sierra
• Manufacturer Part Number: 18-6241
• Material: Magnesium
• Product Type: Sacrificial Anode
• Weight: 0.4 pounds
• Product Dimensions: 0.39 x 0.39 x 0.39 inches
• UPC: 808282103606

Fitment

• R/MR/Alpha One, Sterndrive & Transom Assembly (1983-90) & prior drives
• Alpha One, Gen II (1991 & up)

Replaces (OEM)

• 31640
• 31640A1
• 97-31640Q4
• 31640T6
• 97-31640B4
• 31640A4
• 31640A2
• 316404
• 316403
• 72436A1

Frequently Asked Questions

What is the Sierra 18-6241 anode made of? The Sierra 18-6241 is made of magnesium, which makes it the correct anode type for boats operated in freshwater rather than saltwater.

What drives does the 18-6241 anode fit? It is designed for use on R/MR/Alpha One, Sterndrive and Transom Assembly drives from 1983-90 and prior, as well as Alpha One, Gen II drives from 1991 and up.

Does the 18-6241 cross-reference to a Mercury or MerCruiser part number? Yes, the Sierra 18-6241 replaces Mercury/MerCruiser numbers 31640, 31640A1, 97-31640Q4, 31640T6, 97-31640B4, 31640A4, 31640A2, 316404, 316403, and 72436A1.

How much does the 18-6241 anode weigh? The Sierra 18-6241 magnesium anode weighs 0.4 pounds.

What are the dimensions of the 18-6241 anode? The Sierra 18-6241 measures 0.39 x 0.39 x 0.39 inches.

Why choose a magnesium anode over a zinc anode? Magnesium is more electrochemically active than zinc, which gives the 18-6241 the sacrificial capacity needed to protect drive components in freshwater; zinc anodes are used for saltwater instead.

Is the Sierra 18-6241 a genuine OEM part or aftermarket? The 18-6241 is a Sierra-manufactured aftermarket anode built to meet or exceed the specifications of the original Mercury/MerCruiser equipment it replaces.

How do I know when the 18-6241 anode needs to be replaced? Anodes should be inspected regularly and replaced once roughly half of the original material has corroded away; the 18-6241 is sized as a direct fit for a straightforward swap on applicable MerCruiser drives.

Is the 18-6241 compatible with Alpha One Gen II drives? Yes, in addition to R/MR/Alpha One, Sterndrive and Transom Assembly drives (1983-90 and prior), the 18-6241 fits Alpha One, Gen II drives from 1991 and up.

What comes in the package with the 18-6241? The 18-6241 is supplied as a single magnesium anode.