Sierra 18-3864 Cylinder Head Gasket for Mercury/Mariner V6 2.5L Outboard

The Sierra 18-3864 is a direct-replacement cylinder head gasket engineered for Mercury and Mariner V6 2.5L two-stroke outboard engines. Designed to seal the joint between the cylinder head and engine block, this gasket maintains combustion pressure while sealing critical cooling passages to prevent overheating and water intrusion.

Key Features:

• OEM-quality construction that meets or exceeds Mercury Marine original equipment specifications
• Machined exterior finish for precise sealing and reliable long-term performance
• Sold individually — Mercury V6 engines require one gasket per cylinder head; two are typically needed for a full engine service
• Ideal for use during powerhead rebuilds, cylinder head removal, overheating repairs, or compression loss diagnosis

OEM Interchange Numbers:

• Mercury Marine: 27-184721, 27-822844, 27-822844-1, 27-822844004, 27-8228442, 27-8228443, 27-822844T04, 27-822844T05
• GLM: 35870
• Mallory: 9-63854

Sierra International is a trusted name in marine aftermarket parts, offering an extensive line of precision-engineered components for outboard and inboard marine engines.