Denso 5021 Spark Plug

Denso 5021 U-Groove Spark Plug

Denso 5021 is a conventional spark plug built for older ignition systems that need reliable secondary ignition performance. Its U-Groove ground electrode design improves ignitability, helping support more complete combustion and steady engine operation in compatible Buick, Oldsmobile, and Pontiac applications.

Key Features

• U-Groove ground electrode tip design for improved spark exposure
• Conventional spark plug construction for classic vehicle applications
• 5000 ohm resistor for ignition noise suppression
• Copper center electrode core for efficient heat transfer
• Nickel center and ground electrode tip materials for durable operation
• Tapered seat, 14.00 mm thread diameter, 11.60 mm reach, and 16.0 mm hex size
• Pre-gapped to 1.5 for specified applications

Product Details

This Denso U-Groove Conventional spark plug is engineered around a nickel U-groove ground electrode and copper-core center electrode to support consistent spark delivery in secondary ignition systems. The design increases the spark path exposure at the plug gap, which can improve ignitability and help maintain engine efficiency in the right application. Part number 5021 also cross-references DENSO Auto Parts T14PR-U15 for the same application.

Compatible With 1975-1979 Buick LeSabre, N/A; 1978 Buick Century, N/A; 1977-1978 Buick Regal, N/A; 1977-1978 Buick Skyhawk, N/A; 1977-1978 Buick Skylark, N/A; 1975-1979 Oldsmobile Delta 88, N/A; 1975-1977 Oldsmobile Custom Cruiser, N/A; 1977 Oldsmobile Cutlass, N/A; 1977 Oldsmobile Cutlass Supreme, N/A; 1977 Oldsmobile Omega, N/A; 1977 Oldsmobile Starfire, N/A; 1975-1978 Pontiac Bonneville, N/A; 1975-1978 Pontiac Catalina, N/A; 1975-1978 Pontiac Firebird, N/A; 1975-1978 Pontiac Grand Am, N/A; 1975-1978 Pontiac Grand LeMans, N/A; 1975-1978 Pontiac Grand Prix, N/A; 1976-1978 Pontiac LeMans, N/A; 1977-1978 Pontiac Phoenix, N/A; 1976-1978 Pontiac Sunbird, N/A.

Common Uses

• Rough idle caused by worn or inconsistent spark plugs
• Hard starting in older ignition systems
• Misfire concerns related to weak spark delivery
• Reduced combustion efficiency from aged plugs
• Maintenance replacement for classic Buick, Oldsmobile, and Pontiac engines

Installation Notes

Verify thread diameter, reach, seat type, and heat range before installation. This plug uses a tapered seat and a 14.00 mm thread with 11.60 mm reach, so it should be matched to the engine specification exactly. Check the pre-gap against the vehicle service requirement before installation, and inspect ignition wires, cap, and rotor condition when servicing the plugs.

Quality Assurance

Denso’s U-Groove Conventional line focuses on dependable ignition performance for applications that call for a traditional spark plug design. Part number 5021 is built with nickel and copper electrode materials and a resistor element to support stable operation in the specified fitments.