Audi EA824 (4.0/4.2 V8)

Audi's V8 petrol family — the naturally aspirated 4.2 FSI of the S5, Q7 and A8, and the twin-turbocharged 4.0 TFSI that replaced it in the S8, RS6 and Bentley Bentayga, with the turbochargers mounted inside the vee.

The 4.2 FSI's defining fault is the timing chain, and it is at the rear of the engine — the Volkswagen Group V-engine pattern this catalogue meets repeatedly. Chain tensioner and guide wear produces a rattle on cold start and eventually correlation codes, and reaching it means removing the engine or the gearbox. On an early 4.2 that noise is the diagnosis.

The twin-turbocharged 4.0 brings the hot-vee reality instead: extreme underbonnet heat in a space that is very hard to reach, so wiring, coolant lines and sensors in the vee age faster than their equivalents elsewhere. Both versions are direct-injected and accumulate intake-valve carbon at mileage.