Sierra 18-3863 Head Gasket for Mercury 150 MAR V-6 Outboard Motors

The Sierra 18-3863 is a round head gasket built for Mercury 150 MAR V-6 outboard motors, specifically the production run covering serial numbers 6038681 through C239553. As a critical seal between the cylinder head and powerhead block, the head gasket prevents the loss of compression and keeps combustion gases, fuel, and coolant properly contained within their intended passages. A worn, cracked, or improperly seated head gasket can lead to compression loss, overheating, or coolant intrusion into the cylinders, making this a key maintenance and rebuild component for outboard owners performing a top-end service or full powerhead rebuild.

Sierra manufactures this gasket to meet or exceed the specifications of the original equipment part it replaces, and it is engineered to hold up to the demands of high-horsepower marine engines operating in a harsh saltwater or freshwater environment. The gasket ships as a single round unit finished in white and is intended as a direct fit for the specific Mercury 150 MAR V-6 serial number range noted above, so confirming your engine's serial number against that range before ordering is recommended. Every Sierra part carries the backing of Sierra's customer satisfaction warranty program.

Specifications

• Brand: Sierra
• Manufacturer Part Number: 18-3863
• Product Category: Mercury Outboard Head Gasket
• Fitment: Mercury 150 MAR V-6 outboard, serial numbers 6038681 to C239553
• Cylinder Configuration: V-6
• Shape: Round
• Color: White
• UPC: 030999753717
• Unit Count: 1
• Weight: 0.18 pounds

Fitment

• Mercury 150 MAR, V-6, serial numbers 6038681 to C239553

Frequently Asked Questions

What engine does the Sierra 18-3863 head gasket fit? The 18-3863 is designed for Mercury 150 MAR V-6 outboard motors within the serial number range 6038681 to C239553. Checking your outboard's serial number against that range confirms this is the correct gasket for your engine.

How do I know if my serial number is in range for the 18-3863 gasket? Your Mercury 150 MAR outboard's serial number needs to fall between 6038681 and C239553 for the 18-3863 head gasket to be the correct fit; engines outside that range use a different Sierra head gasket part number.

What shape and color is this head gasket? The Sierra 18-3863 is a round head gasket finished in white.

How much does the 18-3863 head gasket weigh? It weighs 0.18 pounds.

Is the Sierra 18-3863 an OEM part or an aftermarket replacement? The 18-3863 is a Sierra-manufactured replacement gasket engineered to meet or exceed the specifications of the original equipment part it replaces, rather than a part sourced directly from Mercury.

How many gaskets come in the package? One Sierra 18-3863 head gasket ships per unit.

Does the 18-3863 come with a warranty? Yes, the 18-3863 head gasket is covered under Sierra's customer satisfaction warranty program, as are all Sierra parts.

What is a head gasket used for on a Mercury outboard? On a Mercury 150 MAR V-6, the head gasket seals the junction between the cylinder head and the powerhead block, containing compression and preventing combustion gases, fuel, or coolant from leaking between passages.

What are signs I need to replace the 18-3863 head gasket? Loss of engine compression, overheating, or coolant finding its way into the cylinders on a Mercury 150 MAR V-6 are typical indicators that the head gasket, such as the Sierra 18-3863, needs replacement.

Can I use the 18-3863 gasket on a Mercury 150 MAR outside the listed serial range? No, the 18-3863 is matched to the Mercury 150 MAR V-6 serial number range 6038681 to C239553; outboards with serial numbers outside that range require a different head gasket part number.