OM640

Introduced with the second-generation A-Class in 2004 to replace the 1.7-liter OM668, it had to work around the car rather than the other way about: mounted transversely and canted well forward so that it would slide under the sandwich floor in a frontal impact rather than into the footwell. Common rail, four valves per cylinder, twin chain-driven camshafts and turbocharging with an intercooler on every version. The block stayed cast iron — heavier than aluminum, but better suited to the cylinder pressures and quieter with it — under a high-strength aluminum head.

Three outputs covered the range, from the 82-PS A 160 CDI to the 140-PS A 200 CDI and B 200 CDI, and production ran until 2012 with the W169 and W245. Its second career was stranger. Thielert took the OM640 as the basis of the Centurion 2.0 aero-diesel, and Austro Engine did the same for the AE300, which powers Diamond's DA42 twin and DA62 — light aircraft burning jet fuel around the block of a Mercedes hatchback. On the ground, the transversely mountable OM651 took over.