Engine M278.922 Mercedes W218 CLS 500 W212 E 500 300KW 408hp

M278.922 engine—a 4.6L V8 Biturbo—is a powerhouse that defines the “sleeper” performance of the W218 CLS 500 and W212 E 500. While it offers effortless torque and refined power (300kW/408hp), it is an engine that requires very specific due diligence in the used market due to its known architectural “expensive” tendencies.

1. Technical Profile

• Engine Code: M278.922 (DE 46 AL)

• Configuration: 4.6L V8 Twin-Turbocharged

• Output: 300 kW (408 hp) / 600 Nm (443 lb-ft)

• Technology: Direct Injection, Piezo Injectors, Twin-Turbo “Hot V” style (though turbos are side-mounted compared to the newer M177).

• Application: * Mercedes-Benz CLS 500 / CLS 550 (W218)

  • Mercedes-Benz E 500 / E 550 (W212)

2. 2026 Market Valuation (Estimated USD)

By 2026, the price of a used M278 is heavily dictated by a documented Cylinder Bore Inspection.

3. The “M278 Fatal Flaws” Checklist (2026)

If you are buying a complete M278.922, you must verify the status of these three issues, or you risk a total engine loss:

• Cylinder Wall Scoring (Alusil): This is the “End of Life” failure for the M278. The Silitec/Alusil coating on the cylinder walls can fail, leading to oil consumption and knocking. In 2026, do not buy this engine without a borescope video of all 8 cylinders.

• Timing Chain Tensioners & Check Valves: Early M278s suffer from a “clatter” on cold starts. If left unaddressed, the chain stretches and can skip a tooth. Ensure the updated check valves and tensioners are installed.

• Oil in Wiring Harness: The camshaft position sensors and magnets can leak oil through the wires, which eventually wicks its way into the ECU, destroying it. Check the sensor plugs for any trace of oil.

4. Associated Parts to Swap

When installing a complete M278.922, pay attention to these peripherals:

1. Turbochargers: Check for shaft play. At 100k+ km, the wastegate actuators often start to rattle.

2. High-Pressure Fuel Pumps (HPFP): These sit on top of the engine and are prone to failure, causing long cranks and limp mode.

3. Coolant Lines: The plastic turbo coolant lines become extremely brittle. Most owners in 2026 swap these for stainless steel braided lines during an engine replacement.