Mercedes-Benz M111

Mercedes-Benz's 1.8, 2.0 and 2.3 four of the 1990s, including the Kompressor supercharged versions — in the W202 and W203 C-Class, the W210 E-Class, and, under licence, SsangYong's Rexton and Kyron. A fault documented on a C-Class describes those exactly, which is the one thing their owners will not be told anywhere else.

The wiring loom is the fault that defines mid-1990s Mercedes and it is not an engine fault at all. The insulation was biodegradable and becomes brittle, so conductors short against each other and against the engine — producing running faults, sensor codes and no-starts that look like component failures because electrically they are. On any M111 of that era, inspect the loom before condemning a sensor.

The head gasket fails at a corner, typically showing as oil weeping down the side of the block rather than as coolant loss, and the timing chain tensioner and its plastic guides wear enough to rattle at start-up.

The Kompressor adds a supercharger with its own oil, which has no service light and which almost nobody changes — and a clutch that engages it, which fails on its own. A Kompressor that feels like a naturally aspirated car has usually lost the clutch rather than the blower.