The Mercedes D.IV was an eight-cylinder, liquid-cooled inline aircraft engine built by Daimler Motoren Gesellschaft (DMG) and used on a small number of German aircraft during World War I.

The design was based around the pistons of the ubiquitous D.III 6-cylinder design and developed 162 kW (217 hp), making it a Class IV motor under the IdFlieg classification system then in use in Imperial Germany.

When the reliability of the engine proved disappointing, it was supplanted in production by the unrelated six-cylinder Mercedes D.IVa.

Specifically, the long crankshaft used in extending the original straight-six design to a straight-eight proved susceptible to breakage.

Data from [citation needed] Related lists