Mercedes-Benz M156

AMG's naturally aspirated 6.2 V8 — the first engine AMG designed from scratch rather than developing from a Mercedes-Benz block — in the C63, E63, S63, CLS63 and ML63. The cars are badged 63 and the engine is a 6.2, a heritage number rather than a displacement.

Two faults define it and both are expensive. The first is head bolt corrosion: the bolts corrode and stretch, the head loses clamp, and coolant is lost with the usual head-gasket symptoms. Mercedes revised the bolts, so which bolts a given engine has is worth establishing before anything else — a car with the later parts fitted is a materially different proposition.

The second is camshaft and follower wear. The lobes and their followers wear prematurely, and it can be looked at: taking the cam covers off to inspect them is a routine part of buying one of these, not a sign of paranoia. Left alone, debris circulates.

Beyond those, it is a dry-sump-adjacent high-revving engine that is hard on oil, and its later replacement — the M177 / M178 4.0 twin-turbo — shares nothing with it. Anything written about a modern 63 badge describes a different engine entirely.