Opel 1.7 CDTi (CDTi diesels, 1.6 and 1.7)

Opel's 1.7-litre diesel — and an Isuzu design rather than an Opel one, built under the long-standing GM-Isuzu relationship as the 4EE2 and its successors. Fitted to the Astra, Corsa, Meriva and Zafira through two decades.

That origin is genuinely useful: Isuzu material on the 4EE2 applies, and the engine's reputation for mechanical toughness comes from a manufacturer that builds commercial diesels. What lets these engines down is rarely the bottom end.

The recurring faults are the turbocharger's variable-geometry mechanism sticking with carbon, EGR valve blockage, and — on the later CDTi versions — a particulate filter unable to regenerate on the short journeys these cars do. Injector wear producing a rough cold idle completes the list. On the Astra H in particular, glow-plug and glow-module failures are frequent enough that a cold-start complaint should test both before anything else.