Denso 3125 Spark Plug

Denso 3125 U-Groove Spark Plug Overview

The Denso 3125 is a conventional spark plug built for reliable secondary ignition performance in select Mercedes-Benz and Saab applications. Its U-Groove ground electrode design helps improve ignitability, supporting more efficient combustion and consistent engine operation.

As part of the Denso U-Groove Conventional line, this spark plug focuses on practical OE-style performance with a copper center electrode core, nickel center electrode tip, and nickel ground electrode tip. The flat seat, 14.00 mm thread diameter, 19.00 mm reach, and 0.8 pre-gap size make it a direct-spec replacement for the listed vehicles.

Key Features

• U-Groove ground electrode tip design for improved ignitability
• Conventional spark plug construction for everyday engine service
• Copper center electrode core material for stable spark delivery
• Nickel center and ground electrode tip materials
• Flat seat design with 14.00 mm thread diameter
• 19.00 mm reach and 0.8 pre-gap size
• Compatible With 1998 Mercedes-Benz S420, N/A
• Compatible With 1990 Saab 900, N/A
• Compatible With 1988 Saab 900, N/A
• Compatible With 1986-1988 Saab 9000, N/A

Product Details

Denso U-Groove Conventional spark plugs are engineered around a ground electrode shape that exposes the spark more effectively at the gap. For drivers searching for a Denso 3125 spark plug for Mercedes-Benz S420 or a Denso 3125 spark plug for Saab 900 and Saab 9000, this part matches the listed fitment and specifications. The design supports efficient ignition in engines that call for a flat-seat plug with the stated thread, reach, and heat range requirements.

This part cross-references DENSO Auto Parts Q20P-U and Saab 75 05 142, 88 19 294 for the same application.

Common Issues This Part Can Address

• Hard starting caused by worn spark plug electrodes
• Rough idle from inconsistent ignition firing
• Misfire conditions related to degraded plug performance
• Reduced combustion efficiency from excessive electrode wear
• Weak spark delivery in service intervals that call for replacement

Installation Notes

Verify the vehicle’s required thread diameter, reach, seat type, and heat range before installation. Confirm the gap specification against the engine’s service information and inspect the ignition system for wear, fouling, or carbon buildup that could affect plug performance. Use the listed fitment to match the correct application for 1998 Mercedes-Benz S420, 1990 Saab 900, 1988 Saab 900, and 1986-1988 Saab 9000.

Quality Assurance

Denso is known for OE-level ignition component engineering, and the U-Groove Conventional line is built to deliver consistent spark plug performance with application-specific specifications. Part number 3125 is manufactured to the listed dimensions and design details for the confirmed vehicle applications.