Nissan KR20DDET (VC-Turbo, 1.5 and 2.0)

Nissan's 2.0 variable-compression turbo — in the Infiniti QX50 and QX60, and the Altima, X-Trail and Pathfinder.

⚑ It is the only production engine that changes its own compression ratio while running, and that is the whole reason to know its name. A multi-link mechanism between the crankshaft and the connecting rods alters how far the pistons travel — continuously, between about 8:1 and 14:1 — so the engine runs high compression for efficiency at light load and drops it to take boost under power.

There is an extra mechanism between the crank and the pistons that no other engine has, driven by an electric actuator and a control arm. So a knock, a rattle or an oil-pressure fault on one of these has a possible cause that exists nowhere else in this catalogue, and a diagnosis built on ordinary four-cylinder experience is working from an incomplete list of parts.

Its recurring reports are oil-related, which follows from the mechanism: the linkage is lubricated and load-bearing, and oil condition and level matter more here than on a conventional engine of the same size. Nissan's interval and specification are not a suggestion.

It is too new for a settled long-term record, and saying so is more useful than repeating early forum reports — but the design means the stakes of neglect are higher, not merely equal.