Mitsubishi 4D68 (4D6 family, 1.8 and 2.0)

Mitsubishi's 2.0 diesel of the 1990s — in the Galant, the Expo and the Indian-market Mirage.

It is an indirect-injection engine with a mechanical pump, which places it firmly on the far side of the line from everything modern: there is no common rail, no DPF, no EGR cooler and no DPF regeneration to go wrong. Almost every modern diesel complaint is inapplicable here.

What does go wrong is old-diesel wear. Glow plugs and their relay are the commonest cold-start fault and are testable in minutes; the injection pump timing drifts as the belt ages and shows as smoke and poor economy rather than as a running fault; and injector nozzles carbon up and give a knock at idle.

The timing belt drives the injection pump as well as the camshaft, so a belt service on one of these is not the same job as on a petrol engine and getting the pump timing back is the part that takes the skill.

Parts availability is the practical constraint, not the engine — it is durable and slow, and the cars around it usually fail first.