Mercedes-Benz M275 / M279

Mercedes' twin-turbocharged V12 — the M275 and its successor M279 — in the S-class, CL and the Maybach and AMG cars above them.

It is one of very few production V12s left, and almost everything about owning one follows from rarity rather than from any particular weakness: specialist experience is thin even inside the dealer network, and parts are priced for a car that cost what these did.

⚑ Access is the constraint on every job. Twelve cylinders, two turbochargers and their plumbing fill the bay completely, and work that is routine on a V8 requires the front of the car removed. A job priced from a V8 estimate will be wrong.

Its known items are the ones any hot-V twin-turbo has — coolant hoses and turbocharger oil lines that live in heat — plus the ignition coils, of which there are twelve, and a fault on one is proportionally harder to isolate.

The M120 naturally aspirated V12 that preceded it is a different engine, and its results do not carry across.