Sierra 18-0721 Open Dry-Joint Exhaust Gasket, Replaces Mercruiser 27-864547A02/27-864547A01, Fits 4.3L Alpha/Bravo 2002 and Newer

The Sierra 18-0721 is an Open-style dry-joint exhaust gasket engineered as a direct replacement for the original equipment gasket on MerCruiser 4.3L Alpha/Bravo sterndrive applications built 2002 and newer without engine catalyst. Dry-joint gaskets seal the mating surface between the exhaust manifold and riser, and choosing the correct style matters: this is the Open variant, part of a three-style family (Open, Closed, and Restricted) that all share a common mounting footprint but differ in how they route exhaust flow. Installing the wrong style can affect engine cooling and exhaust backpressure, so confirming 18-0721 against your existing gasket or manufacturer reference before ordering is important.

This gasket is round in shape and finished in white, and is sold as a single unit for one exhaust joint. It directly replaces the Mercruiser OEM gasket numbers 27-864547A02 and 27-864547A01, so it can be used as a drop-in service part during manifold or riser replacement, tune-up, or routine maintenance where the old dry-joint seal has failed or is showing signs of leakage or corrosion. Sierra manufactures the 18-0721 to meet or exceed the specifications of the original equipment part it replaces, making it a reliable choice for engine and drive maintenance in the demanding marine environment.

Specifications

• Brand: Sierra
• Manufacturer Part Number: 18-0721
• Item Type: Dry Joint Gasket (Open)
• Shape: Round
• Color: White
• Weight: 0.25 pounds
• UPC: 808282359454
• Fits: 4.3L Alpha/Bravo (2002 and newer without engine catalyst)
• Related Gasket Styles: 18-0720 (Closed), 18-0722 (Restricted)
• Replaces (OEM): 27-864547A02, 27-864547A01

Fitment

• Mercruiser 4.3L Alpha/Bravo sterndrive, 2002 and newer, without engine catalyst

Replaces (OEM)

• 27-864547A02
• 27-864547A01

Frequently Asked Questions

What does the Sierra 18-0721 gasket fit? The 18-0721 is designed for MerCruiser 4.3L Alpha/Bravo sterndrive applications built 2002 and newer without engine catalyst.

What OEM part numbers does the 18-0721 replace? It replaces Mercruiser 27-864547A02 and 27-864547A01, making it a direct swap for either of those original equipment gasket numbers.

Is 18-0721 the Open, Closed, or Restricted dry-joint gasket? 18-0721 is the Open-style dry-joint gasket. Sierra also offers 18-0720 as the Closed style and 18-0722 as the Restricted style for the same joint.

How much does the 18-0721 gasket weigh? The gasket weighs 0.25 pounds.

What color and shape is the 18-0721 gasket? It is round in shape and white in color.

Does the 18-0721 come with mounting hardware? The 18-0721 is sold as a single gasket unit; it does not include the manifold, riser, or fastening hardware.

How do I know if I need the Open, Closed, or Restricted version? Match the style to the gasket currently installed or to your manifold and riser specification, since 18-0720, 18-0721, and 18-0722 share a mounting footprint but route exhaust flow differently.

Is the Sierra 18-0721 genuine OEM or aftermarket? The 18-0721 is a Sierra-manufactured replacement part, built to meet or exceed the specifications of the Mercruiser 27-864547A02/27-864547A01 gasket it replaces.

Will 18-0721 fit a 4.3L engine with a catalyst-equipped exhaust? No, this gasket is specified for 4.3L Alpha/Bravo applications 2002 and newer without engine catalyst.

What is the UPC for the Sierra 18-0721? The UPC for Sierra 18-0721 is 808282359454.