Sierra 18-0550 Plug Off Cap, Replaces OMC 909830, 1-1/4 Inch

The Sierra 18-0550 Plug Off Cap is a plastic plug cap used to seal an unused port on marine exhaust manifold applications. It is sized for a 1-1/4 inch (31.8mm) opening and is molded in white plastic for durability in the marine engine compartment environment. This cap is designed as a direct aftermarket equivalent to OMC 909830, meeting or exceeding the performance of the original equipment part it replaces.

The 18-0550 is a simple, purpose-built component: a single plug that presses or threads into place to close off an exhaust manifold port that is not being used in a given engine configuration, keeping the cooling and exhaust system sealed properly. Because it is interchangeable with several OEM and aftermarket cross-reference numbers, it can be used to service a range of OMC, Evinrude/Johnson, GLM, and Mallory-numbered applications that call for this same 1-1/4 inch plug cap. Each unit ships as a single cap ready to install.

Specifications

• Brand: Sierra
• Manufacturer Part Number: 18-0550
• Product Name: Plug Off Cap
• Material: Plastic
• Color: White
• Inside Diameter: 1-1/4 inch (31.8mm)
• Weight: 0.08 pounds
• Quantity: 1 plug off cap per unit
• OEM Cross Reference: GLM 22280, Evinrude/Johnson 909830, 3852476, Mallory 9-42721, OMC 909830

Fitment

Fits applications calling for a 1-1/4 inch (31.8mm) exhaust manifold plug off cap, including those originally equipped with OMC 909830 or 3852476.

Replaces (OEM)

• GLM 22280
• Evinrude/Johnson 909830
• 3852476
• Mallory 9-42721
• OMC 909830

Frequently Asked Questions

What is the Sierra 18-0550 Plug Off Cap used for? The Sierra 18-0550 is a plastic plug cap that seals an unused 1-1/4 inch exhaust manifold port on applicable marine engines, keeping the exhaust and cooling passages closed off where a fitting is not installed.

What size is the Sierra 18-0550 plug off cap? It has a 1-1/4 inch (31.8mm) inside diameter, sized to fit the port opening it is designed to seal.

Does the 18-0550 replace OMC 909830? Yes, the Sierra 18-0550 is interchangeable with OMC 909830 and is built to meet or exceed the performance of that original equipment part.

What other part numbers cross-reference to the Sierra 18-0550? The 18-0550 is interchangeable with GLM 22280, Evinrude/Johnson 909830, Evinrude/Johnson 3852476, Mallory 9-42721, and OMC 909830 and 3852476.

What material is the Sierra 18-0550 plug off cap made from? It is made of white plastic, a lightweight material suited to sealing exhaust manifold ports in the marine engine compartment.

Is the Sierra 18-0550 genuine OEM or aftermarket? It is a Sierra aftermarket part manufactured to meet or exceed the specifications of the original equipment part it replaces, such as OMC 909830.

How many plug off caps come in one Sierra 18-0550 package? One Sierra 18-0550 plug off cap is included per unit.

How much does the Sierra 18-0550 plug off cap weigh? The 18-0550 weighs 0.08 pounds.

Can the 18-0550 be used in place of a Mallory 9-42721 cap? Yes, the Mallory 9-42721 is one of the cross-reference numbers the Sierra 18-0550 is interchangeable with.

Is the Sierra 18-0550 threaded or a press-fit plug? The 18-0550 is a plug off cap sized to a 1-1/4 inch (31.8mm) opening; specific thread or press-fit installation details beyond that sizing are not specified.