Hyundai U-family (CRDi, 1.5 and 1.7)

The Hyundai Motor Group's small common-rail diesels, in 1.1, 1.4, 1.5 and 1.6 litre forms — the CRDi engines of the i20, i30, Accent, Rio, Cee'd and Tucson, and the diesel counterpart to the Gamma petrol family.

They are chain-driven and generally durable, and the recurring complaints come from the emissions hardware rather than from the engine: EGR valve and cooler blockage, and a particulate filter that cannot regenerate on the short journeys these cars typically do. The consequence to catch early is oil dilution — a rising level rather than a falling one, which owners rarely read as a fault.

The 1.6 in particular is widely used and well documented. On higher-mileage examples the turbocharger's variable-geometry mechanism sticking with carbon is the frequent finding, and it often frees with cleaning rather than requiring replacement — worth attempting before quoting a unit.