Sierra 18-0539 Rubber Seal Gasket - Replaces Mercury 37721

The Sierra 18-0539 Rubber Seal Gasket is a rubber exhaust leg seal used in Mercury outboard cooling systems. It is designed as a direct replacement for the original equipment seal, restoring a tight, leak-free connection where the exhaust leg meets the powerhead cooling passages. A worn or hardened rubber seal in this location can allow water or exhaust gases to escape past the joint, so replacing it with a properly sized gasket like the 18-0539 helps maintain correct sealing pressure and cooling system integrity.

Made of rubber, this seal is compact and precisely sized to fit its intended mounting location, with dimensions of 0.39 x 0.39 x 0.39 inches and a weight of 0.07 pounds. It is built to meet or exceed the quality of the original equipment part it replaces, making it a reliable choice for routine maintenance or repair of the exhaust cooling seal. This is a small, low-cost component, but correct fitment matters since it is engineered as a like-for-like replacement for Mercury 37721.

Specifications

• Brand: Sierra
• Manufacturer Part Number: 18-0539
• Product Name: Rubber Seal Gasket
• Material: Rubber
• Weight: 0.07 pounds
• Product Dimensions: 0.39 x 0.39 x 0.39 inches
• UPC: 030999874474

Replaces (OEM)

• Mercury 37721

Frequently Asked Questions

What is the Sierra 18-0539 used for? The Sierra 18-0539 is a rubber seal gasket used in the exhaust leg area of Mercury outboard cooling systems, sealing the joint to prevent water or exhaust leaks.

Is the Sierra 18-0539 a direct replacement for Mercury 37721? Yes, the 18-0539 is manufactured as a direct replacement for Mercury part 37721.

What material is the 18-0539 seal made from? It is made of rubber, which allows it to compress and form a tight seal against mating surfaces.

How much does the Sierra 18-0539 gasket weigh? This gasket weighs 0.07 pounds.

What are the dimensions of the 18-0539 rubber seal? The seal measures 0.39 x 0.39 x 0.39 inches.

Does the Sierra 18-0539 meet OEM quality standards? Sierra manufactures the 18-0539 to meet or exceed the quality of the original equipment Mercury 37721 seal it replaces.

What is the UPC for the Sierra 18-0539 gasket? The UPC for the Sierra 18-0539 Rubber Seal Gasket is 030999874474.

Is the 18-0539 only for Mercury outboards? The 18-0539 is designed to replace the Mercury 37721 seal used in Mercury outboard cooling systems.

What comes in the package with the 18-0539? The Sierra 18-0539 is sold as a single rubber seal gasket.

Why would I need to replace this rubber seal? Over time the rubber in an exhaust leg seal like the 18-0539 can harden or crack, allowing leaks; replacing it with a new Sierra 18-0539 restores a proper seal.

Can the Sierra 18-0539 be reused after removal? No, once a rubber seal gasket like the 18-0539 is compressed and removed it typically loses its sealing ability and should be replaced with a new one.