7. Mercedes-Benz OM617 Diesel
The Mercedes-Benz OM617 diesel is the stuff of legend among longevity enthusiasts.
Found in classic W123 models, this five-cylinder engine is renowned for surpassing 500,000 miles—and sometimes even more—with proper care.
As Hemmings notes, the OM617’s simple mechanical fuel injection and robust construction make it a favorite for those seeking a true lifetime companion.
Its reputation for durability has earned it a devoted following worldwide.