1998–2005 Mercedes-Benz M-Class

1998-2005 Mercedes-Benz M-Class — Spark Plug Replacement

By Tom Becker ✓ Certified Mechanic · Published Sep 24, 2026 · Updated Oct 14, 2026

🔧🔧🔧 Advanced 90-120 minutes $208 DIY

Save $1,733 by doing it yourself! Shop cost: $1,941

Quick answer: Spark Plug Replacement on a 1998–2005 Mercedes-Benz M-Class is rated Advanced and takes about 90-120 minutes. You'll need 5 tools for this job, and parts cost about $208. This guide walks you through the full job step by step, including the mistakes to avoid.

Quick Video Tutorial

Parts You Need

Total Cost

$0.00

Part Name	Part Number	Price	Buy
Spark plugs for M112/M113 (check quantity: 12 for V6, 16 for V8)	—	—	Amazon

💡 Pro tip: Order all parts at once to save on shipping

Step-by-Step Instructions

Follow these steps carefully

Cool down and access

Let the engine cool completely overnight if possible. Disconnect the negative battery terminal. On the W163 M-Class the plugs are on the sides of the engine under the coil packs. Remove the engine covers to access them.

Disconnect coil connectors

Working one bank at a time, disconnect the electrical connector from each coil pack. The connectors have release tabs that must be pressed. Set the wiring aside carefully - the insulation is old and brittle.

Remove the coil packs

Remove the bolts holding each coil pack and pull the coils straight out. On the M113 V8 there are two plugs per cylinder, so you will see paired coils. Place removed coils in order on a clean surface.

🔧 Mechanic's note — Ray Delgado

Here's what I know: on the M113 V8 you're doing 16 plugs — two per cylinder. Work one bank at a time and keep the coils in order; losing track halfway through a 16-plug job is a long day.

Clear the plug wells

Blow compressed air into each plug well to clear accumulated grit. This is critical on the W163 - debris falls directly into the cylinder if you skip this. Work on one plug at a time, keeping others covered.

Remove and inspect old plugs

Remove each plug with a 16mm spark plug socket. Inspect the old plugs - a tan insulator is normal. Oil fouling indicates valve cover gasket leaks, common on high-mileage M112/M113 engines. Confirm new plug gap matches spec.

🔧 Mechanic's note — Tom Becker

In my experience, if you find oil fouling on the plugs, that's valve cover gaskets leaking — common on high-mileage M112/M113 engines. New plugs won't fix an oil-fouled cylinder for long.

Install new plugs

Thread each new plug in by hand until finger-tight to avoid cross-threading the aluminum head. Then torque to 25 Nm. On the V8, repeat for all 16 plugs - do not rush this step.

Reinstall coils and verify

Reinstall all coil packs and torque their bolts. Reconnect every electrical connector until it clicks. Reconnect the battery. Start the engine - it should idle smoothly with no misfire codes.

All Done!

Test your repair before closing everything up. If something doesn't work right, double-check your steps.

⚠️ Common Mistakes to Avoid

• Using the wrong plugs - the M112 V6 and M113 V8 in the W163 use specific copper or platinum plugs; verify by engine code.
• Cross-threading plugs in the aluminum heads - always start them by hand.
• Over-tightening - 25 Nm max on these aluminum heads.
• Forgetting the W163 V8 has 16 spark plugs (two per cylinder) - buy enough.