Peugeot XU (XU7 / XU10)

PSA's larger petrol four — 1.6 to 2.0 litres as the XU5, XU7, XU9 and XU10 — in the 205 GTI, 306, 405, 605 and Citroën's BX and Xantia.

It did not stop being built when Peugeot stopped building it, and that is the reason this page matters. Iran Khodro has made the XU7 under licence for decades: it is the engine of the Peugeot 405, Pars, Samand and Arisun, and it is among the most numerous engines on Iranian roads. A fault documented on a 1990s French car describes a car built last year, which nothing published in either place tends to say.

It is belt-driven and it is an interference design. A snapped belt bends valves, so the interval is a date rather than a suggestion — and on a thirty-year-old car or a hard-worked taxi, belt history is the unknown that matters most.

On the bi-fuel conversions the exhaust valves are the wear item. A great many of these engines run on compressed natural gas, which burns hotter and drier than petrol; valve seat recession and burnt exhaust valves appear far earlier on a CNG car than the same engine on petrol, and a compression test tells you which history a given engine has actually had.

Otherwise it is simple and long-lived: the head gasket goes on anything that has been allowed to overheat, and running faults are ignition and fuel rather than anything internal.