Mercedes-Benz M266

The naturally aspirated four of the W169 A-Class and W245 B-Class, in 1.5, 1.7 and 2.0 litre forms — the last of Mercedes-Benz's sandwich-floor small cars before the platform changed completely.

It is a simple, port-injected, chain-driven engine, and its own faults are modest. The complaints that dominate these cars are the CVT rather than the engine: the autotronic transmission behind many of them produces flaring, hesitation and loss of drive that arrive described as engine problems. Separate an engine-speed symptom from a road-speed one before opening anything.

Where the engine is at fault, the recurring items are the camshaft adjuster, the crankcase ventilation system — which blocks and pushes oil past seals in the usual way — and the ignition coils. The sandwich-floor construction makes access poor for the work, which is worth telling an owner before the estimate rather than after.