Mercedes-Benz S-Class: M278 4.6TT Biturbo Timing Chain Cold-Start Rattle

The M278 4.6-litre twin-turbocharged V8 petrol engine in the W222 S500 and S450 is affected by timing chain cold-start rattle caused by tensioner oil drain-back after extended parking. Like the M276, the engine uses dual chains per bank and the tensioner design allows oil pressure to drop, letting the chain go momentarily slack on start-up. Widely documented on international Mercedes forums and confirmed by AU and NZ independent specialists. While some cases are a cold-start noise that clears within seconds without immediate damage, others indicate progressive chain wear requiring full timing chain service involving significant labour due to engine access.

• Audible rattle from front of engine for first 5 to 20 seconds on cold start
• Check engine light with P0008, P0016, or bank timing correlation codes
• Reduced power or rough idle if chain has jumped a tooth
• Oil consumption higher than factory specification

1. 1

   Cold-start only — engine must have been off overnight.

2. 2

   Listen immediately for a chain rattle at the front of the engine and record on video.

3. 3

   Pull diagnostic codes for timing correlation faults on both banks.

4. 4

   Ask for prior service history and whether tensioners or chains have been replaced.

5. 5

   V8 timing chain jobs are substantially more expensive than four-cylinder equivalents due to access.

Parts involved: Timing chain.

$4,000 to $9,500 at New Zealand independent workshop rates. That is for this job on its own, not for the car.

An estimate, in NZD, for the repair as normally carried out. What a specific car costs depends on which part has failed and what it damaged on the way — treat this as the floor for a negotiation, not a quote.

• “Has the engine ever rattled on cold start?”
• “Have the timing chains or tensioners been inspected or replaced?”
• “Are there any stored engine fault codes?”

The failure described above is documented in published sources — owner forums, technical service bulletins, recall notices and workshop write-ups — held in our fault database. The inspection instructions and the cost estimate are KickTyres’ own interpretation of them, and it is a starting point for an inspection rather than a manufacturer statement.