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Autopapyrus · Mercedes-Benz M-Class 3.2 V6 M112 (2000)
https://autopapyrus.com/guides/mercedes-benz/m-class/spark-plug-replacement/
Compiled automatically from service literature and owner experience. Specs are for the typical configuration — check them against your exact car before you start.

Mercedes-Benz M-Class 3.2 V6 M112 (2000): Spark Plug Replacement

The M112 engine has two spark plugs per cylinder, 12 in total. The plugs sit deep in the aluminum cylinder heads, so do this job only on a completely cold engine, or you risk stripping the threads. The typical replacement interval is about 60,000 km or per the maintenance schedule. A thin-wall socket and careful handling matter more than force.

Difficulty: Medium Time: 2-3 hours Steps: 10 Tools: Thin-wall spark plug socket with extension and universal joint (size to match your plugs), torque wrench 20-40 N·m (15-30 lb-ft), sockets and ratchet for removing decorative covers and air ducts, spark plug boot or coil puller, compressed air, copper or ceramic anti-seize for the threads only if the spark plug manufacturer allows it, flashlight

Part

  • 🔩 12 spark plugs (two per cylinder, Twin Spark system) from NGK, Bosch or Beru, suitable for the M112 3.2. Use the catalog for your VIN to get the exact part numbers, so you get the correct gap and size. Also replace the spark plug well seals or boots if they have hardened

Step by step

10 steps
  1. Let the engine cool completely, preferably overnight. Disconnect the negative battery terminal. Keep in mind that on a 2000 model-year vehicle, the radio and clock settings may be lost.
  2. Remove the decorative engine cover and any plastic air ducts or intake components that block access. Label or photograph every connector and hose you disconnect.
  3. Disconnect the electrical connectors from the coils and the wiring harness. Remove the spark plug boots and wires without pulling on the wire. Grip the boot itself and rock it loose. Remember or label which coil and wire belongs to which cylinder.
  4. Thoroughly blow out the spark plug wells with compressed air. No dirt should fall into the cylinders when you unscrew a plug.
  5. Unscrew the plugs with the thin-wall socket and extension. Start turning smoothly. If a plug feels tight, thread it back in slightly, apply penetrating oil, wait, and try again. Do not apply force with a sudden jerk.
  6. Inspect the removed plugs. Even, light brown deposits indicate normal operation. Oil, soot or a white coating points to a mixture or oil problem.
  7. Check the gap of the new plugs and compare it with the value specified by the spark plug manufacturer. Do not bend the side electrode much.
  8. Thread the new plugs in by hand until they stop. Then tighten them with a torque wrench to about 28 N·m (21 lb-ft). Do not overtighten, because aluminum threads strip easily.
  9. Check the condition of the spark plug boots and wires. Cracks, signs of arcing, or oil inside the wells mean they need to be replaced too. Push the boots on until they click.
  10. Reconnect the connectors, then install the air ducts and the cover. Reconnect the battery, start the engine, and check that it runs smoothly without misfires and that there are no misfire fault codes.

Common mistakes and warnings

  • Work only on a cold engine. Spark plugs in the aluminum M112 heads tend to seize if they go unreplaced for a long time. If the threads are stripped, the cylinder head will need repair, so do not force tight plugs. If you are not confident, leave the job to a repair shop.