Peugeot DV6 (1.6 HDi)

PSA's 1.6-litre common-rail diesel, developed with Ford — which is why the same engine appears across Peugeot, Citroën, Mini, Volvo, Mazda and Ford as the 1.6 TDCi or DV6. It is one of the most widely fitted diesel engines in Europe, and knowledge about it transfers directly across all those badges.

Its characteristic failure is the turbocharger, and the cause is usually oil supply rather than the turbocharger itself: the oil feed pipe's restrictor screen blocks with carbon, the bearing is starved, and the turbocharger fails. Fitting a replacement without cleaning or renewing the feed and clearing the sump destroys the new one too — this is the single most repeated expensive mistake on this engine.

The diesel particulate filter and its additive system on the earlier cars, EGR blockage and — on short-journey use — oil dilution complete the picture. As with every filter-equipped diesel here, duty cycle explains more than mileage does.