Denso 4187 Spark Plug

Denso 4187 U-Groove Spark Plug Overview

The Denso 4187 is a conventional spark plug from Denso’s U-Groove line, built for drivers who want reliable ignition performance and consistent engine operation. Its U-groove electrode design helps improve ignitability, which supports smoother combustion and better engine efficiency in the right application.

For buyers searching for a Denso spark plug for Honda Civic or other secondary ignition service parts, this plug combines a copper core center electrode, nickel tip materials, and a standard ground configuration for straightforward OE-style replacement service.

Key Features

• Part number: 4187
• Denso U-Groove Conventional spark plug design
• U-groove electrode profile for improved ignitability
• Copper core center electrode for stable heat transfer
• Nickel center and ground electrode tip materials
• 5000 ohm resistor for ignition system noise control
• Pre-gapped to 0.8 mm
• Flat seat, 14.00 mm thread diameter, 19.00 mm reach
• 16.0 mm hex size for standard service tools
• Manufacturer heat range: 31

Product Details

Denso’s U-Groove Conventional line focuses on dependable spark delivery with a design that exposes more of the air-fuel mixture to the spark kernel. The Denso 4187 uses a standard single ground electrode, nickel ground tip, and copper core center electrode to support consistent ignition performance in the specified application. If you are replacing worn ignition components on a Honda Civic or similar vehicle that calls for this specification, this spark plug is built to match the required thread, reach, seat type, and gap.

This part cross-references DENSO Auto Parts U31ESR-N for the same application.

Common Problems This Part Can Address

• Hard starting caused by worn spark plug electrodes
• Rough idle from weak or inconsistent spark output
• Misfire symptoms related to aged secondary ignition components
• Reduced fuel efficiency from incomplete combustion
• Engine hesitation during acceleration

Installation Notes

Verify the required thread diameter, reach, seat type, and pre-gap before installation. The Denso 4187 is pre-gapped at 0.8 mm, but final gap verification is still recommended during service. Use the correct 16.0 mm spark plug socket and follow the vehicle manufacturer’s torque specification for the engine.

For fitment-based searches, this part is commonly referenced for Honda Civic spark plug replacement and other applications that specify the same Denso 4187 configuration. Always confirm the engine’s ignition specification before installation.

Quality Assurance

Denso manufactures this spark plug as part of its U-Groove Conventional product line, using a conventional nickel-and-copper electrode construction and a resistor design suited to standard ignition service. The part is built to the listed specifications for direct replacement use in the correct application.