Mercedes-Benz M278

Mercedes-Benz's 4.7-litre turbocharged V8 for the standard range, with the turbochargers mounted inside the vee. Its AMG counterpart of the same generation is the M157 at 5.5 litres, and both are the direct predecessors of the M177/M178 that replaced them.

The hot-vee layout brings the same reality as its successor: everything between the banks runs extremely hot and is very hard to reach. Heat-cycled wiring, coolant lines and sensors in that space fail earlier than their equivalents on a naturally aspirated V8, and labour dominates any estimate.

The fault most specific to it is camshaft adjuster and timing-chain wear, presenting as a start-up rattle and eventually correlation codes, plus oil leaks from the turbocharger oil lines into the vee where they are difficult to see and easy to misattribute. Direct injection adds the usual intake-valve carbon at mileage.