NGK — BPR6EFS Standard Marine Spark Plug — 901421

NGK BPR6EFS Standard Marine Spark Plug — Stock No. 3623

The NGK BPR6EFS is a standard marine spark plug for verified gasoline inboard and sterndrive applications. Its copper core supports heat dissipation, while the corrosion-resistant trivalent metal plating and high-strength ceramic insulator are designed for dependable marine ignition service. Confirm the exact engine model and serial number before ordering.

Part Details

• Brand: NGK
• NGK Part Number: BPR6EFS
• NGK Stock Number: 3623
• Mercury/Quicksilver Reference: 816336Q
• Product Type: Standard marine spark plug
• System: Ignition
• Thread Diameter: 14.0 mm / 0.551 in
• Thread Length: 17.5 mm / 0.689 in
• Socket Size: 16 mm / approximately 5/8 in
• NGK Reference Gap: 0.8 mm / approximately 0.032 in

Compatible Applications

• MerCruiser 3.0L / 181 CID: From serial 0L010042
• MerCruiser 4.3L Gen+: From serial 0L010065
• MerCruiser 4.3L EFI Gen+: From serial 0L012009
• MerCruiser 5.0L EFI Gen+: From serial 0L015751
• MerCruiser 5.7L EFI Gen+: From serial 0L010035
• MerCruiser 5.7L Gen+: From serial 0L010037
• MerCruiser 350 MAG MPI Gen+: Including serial range 0L002600–0L309999
• MerCruiser 7.4L MPI: From serial 0L002006
• Volvo Penta: 4.3L Gi EFI, 4.3L GL 2-barrel, 5.0L Fi, 5.7L GSi Gen 1+, 5.8L FSi EFI HO, and 7.4L Gi L29
• Additional marine applications: Selected OMC, Indmar, and Marine Power gasoline engines
• Always confirm the engine model and serial number in the engine owner's manual before ordering.

Key Features

• Copper-core construction: Promotes effective heat dissipation in marine gasoline engines.
• Corrosion-resistant plating: Trivalent metal plating helps resist corrosion and thread seizure.
• Durable insulator: High-strength alumina-silicate ceramic supports reliable ignition performance.
• Triple-seal design: Helps protect the plug's internal construction.
• Removable terminal: Supports the applicable marine ignition connection.

Replacement and Installation Guidance

• Replace spark plugs according to the engine manufacturer's maintenance schedule or when inspection shows electrode wear, fouling, corrosion, a damaged insulator, or an incorrect gap.
• Hard starting, ignition misfire, and rough running can indicate that the plugs and ignition system need inspection.
• For engines using multiple plugs, replacing the complete set together helps maintain consistent ignition performance.
• Check the required gap against the engine manufacturer's specification before installation, even when the plugs are supplied pre-gapped for an applicable application.
• Use the correct spark-plug socket and follow the engine manufacturer's tightening procedure.

Technical FAQ

• Is BPR6EFS compatible with every 3.0L, 4.3L, 5.0L, 5.7L, or 7.4L marine engine? No. Engine generation, ignition system, and serial number can change the required spark plug.
• What is the reference spark gap? NGK lists 0.8 mm / approximately 0.032 in for the applicable marine applications shown.
• Is 816336Q the same plug? Mercury/Quicksilver 816336Q is the listed OEM reference for the BPR6EFS standard spark plug. Confirm it against the exact engine before ordering.
• Should the full set be replaced together? For engines using multiple plugs, replacing the complete set together helps keep ignition performance consistent across cylinders.
• Do I need to check the gap before installation? Yes. Confirm the engine manufacturer's required gap before fitting.

Parts Desk Insights

• Best use case: Verified marine gasoline inboard and sterndrive applications that call for NGK BPR6EFS or the 816336Q reference.
• Common issue: Matching by engine displacement alone can lead to the wrong plug. Generation and serial number are essential for fitment.
• Installation reminder: Check the required gap, use the correct socket, and follow the engine manufacturer's tightening procedure.