Sierra Water Tube Guide 18-3221, Replaces 23-816583, for MerCruiser Gen II

The Sierra 18-3221 Water Tube Guide is a cooling system component engineered for MerCruiser Gen II sterndrive applications. It directs cooling water flow through the drive unit as part of the raw water circulation path, and is molded from durable white polypropylene (PP) for resistance to corrosion and degradation in the marine cooling environment. With a compact outside diameter of 1.49 inches, an item length of 1.25 inches, and a nominal wall thickness of 0.12 inches, this water tube guide is sized to fit precisely in place of the original equipment part it replaces.

As a direct-fit replacement, the Sierra 18-3221 cross-references to OEM part number 23-816583, letting owners restore proper cooling water flow without sourcing an original equipment part. It is built to Sierra's quality standard for MerCruiser Gen II cooling system service, making it a straightforward maintenance or repair item when a water tube guide has cracked, degraded, or is being replaced as part of a broader cooling system overhaul.

Specifications

• Brand: Sierra
• Manufacturer Part Number: 18-3221
• Product Name: Water Tube Guide
• Material: Polypropylene (PP)
• Color: White
• Outside Diameter: 1.49 inches
• Item Length: 1.25 inches
• Nominal Wall Thickness: 0.12 inches
• Weight: 0.04 pounds
• UPC: 808282243876
• Fitment: MerCruiser Gen II
• OEM Cross Reference: 23-816583

Fitment

For MerCruiser Gen II sterndrive units.

Replaces (OEM)

23-816583

Frequently Asked Questions

What does the Sierra 18-3221 Water Tube Guide fit? The Sierra 18-3221 is designed for MerCruiser Gen II sterndrive applications, where it guides cooling water flow through the drive unit.

What OEM part number does 18-3221 replace? Sierra 18-3221 replaces OEM part number 23-816583, so it can be installed as a direct substitute for that original equipment water tube guide.

What material is the water tube guide made from? It is molded from white polypropylene (PP), a plastic chosen for its resistance to corrosion and degradation in a marine cooling water environment.

How big is the Sierra 18-3221 Water Tube Guide? It has an outside diameter of 1.49 inches, an item length of 1.25 inches, and a nominal wall thickness of 0.12 inches.

How much does part 18-3221 weigh? The Sierra 18-3221 Water Tube Guide weighs 0.04 pounds.

Is the Sierra 18-3221 a genuine OEM part or an aftermarket replacement? It is a Sierra-branded aftermarket replacement part manufactured to match the fit and function of OEM part 23-816583.

Will this water tube guide fit a MerCruiser Gen I drive? The Sierra 18-3221 is specified for MerCruiser Gen II applications; fitment for other drive generations is not listed for this part number.

What is the UPC for the Sierra 18-3221 Water Tube Guide? The UPC for the Sierra 18-3221 Water Tube Guide is 808282243876.

Why would I need to replace the water tube guide in the cooling system? A cracked, worn, or degraded water tube guide can disrupt raw water flow through the MerCruiser Gen II drive, so replacing it with the Sierra 18-3221 restores proper cooling water circulation.

Does the 18-3221 come as a single piece? Yes, the Sierra 18-3221 Water Tube Guide is supplied as a single unit count item.