NGK Spark Plug – DPR6EA-9

The NGK DPR6EA-9 is a standard copper-core nickel spark plug used in select marine outboards, motorcycles, ATVs, utility vehicles, and small-engine applications where the manufacturer specifies the DPR6EA-9 / NGK 5531 plug profile. It features a resistor design to help reduce ignition noise and radio frequency interference, along with a projected insulator nose for consistent combustion-chamber spark positioning in compatible engines.

This plug should be installed only where the engine service manual, ignition label, or application chart specifically calls for NGK DPR6EA-9, NGK 5531, or an approved equivalent.

Key Features

• Genuine NGK standard spark plug.
• NGK part number: DPR6EA-9.
• NGK stock number: 5531.
• Copper-core nickel construction for standard service applications.
• Resistor-style plug to help reduce ignition-related electrical interference.
• Projected insulator nose design.
• Thread diameter: 12 mm.
• Thread reach: 19 mm / 3/4 in.
• Hex size: 18 mm.
• Seat style: flat / gasket seat.
• Heat range: 6.
• Factory preset gap: 0.036 in. / 0.9 mm.
• Threaded terminal configuration.

Application Compatibility

Common application context includes select marine, motorcycle, ATV, and utility-engine applications where the factory plug chart calls for NGK DPR6EA-9 / 5531, including:

• Select Mercury / Mariner 9.9 HP FourStroke outboard applications where specified
• Select Mercury applications using 827858Q / 33-827858 plug references where confirmed by parts chart
• Select Yamaha F15 / F20 / F25 / T25 outboard applications where specified
• Select Honda motorcycle and ATV applications where specified
• Select Kawasaki, Suzuki, Triumph, and other powersports applications where the plug chart calls for this profile

Use this spark plug only where the manufacturer’s application chart specifically lists DPR6EA-9, 5531, or an approved equivalent.

Fitment Notice

Confirm fitment by exact engine model, serial number, year, service manual, and factory spark plug chart before ordering. Spark plugs with the same thread diameter can still differ in reach, heat range, seat style, terminal style, projected-tip design, resistor specification, and required gap. Installing the wrong plug can cause hard starting, misfire, poor idle, overheating, thread damage, piston contact, or ignition-system issues.

When This Part Needs Replacement

Replace spark plugs during scheduled tune-up service or whenever the plug is worn, fouled, fuel-soaked, oil-contaminated, cracked, corroded, damaged, or causing hard starting, rough idle, hesitation, misfire, weak acceleration, or poor low-speed running. Marine outboards that troll, idle for long periods, or operate in damp and salt-air environments should have spark plugs inspected more regularly.

Installation Notes

Check the plug number and gap against the engine service chart before installation. Install into clean, undamaged cylinder head threads and tighten to the manufacturer’s torque specification for the exact engine. Because this is a gasket-seat plug, confirm the sealing washer is present and seats properly. Avoid adding anti-seize unless the engine or plug manufacturer specifically calls for it, as lubricant can change clamping load and increase the risk of over-tightening.

Alternate/Superseded Part Numbers

• NGK DPR6EA-9 spark plug part number
• NGK 5531 NGK stock number
• DPR6EA9 alternate catalog formatting
• Mercury 827858Q marine reference; verify by engine serial number and plug chart
• MerCruiser / Mercury 33-827858 marine reference; verify by engine serial number and plug chart
• Yamaha 94701-00375 cross-reference; verify by model and plug chart
• Yamaha 94700-00375 cross-reference; verify by model and plug chart

Parts Desk Insight

The DPR6EA-9 is a 12 mm, gasket-seat plug with a projected tip and 0.9 mm preset gap. It should not be substituted based only on horsepower, brand, or heat range. Matching the exact plug number to the engine’s service chart helps avoid incorrect reach, sealing style, or gap issues that can lead to misfire, thread damage, or poor running.

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