What can kill an old Mercedes-Benz W140 with an inline-six diesel? Not much, generally speaking. However, pushing one to its limits on the Autobahn at full throttle for extended periods certainly doesn't help. Ignoring a rising temperature gauge is also a surefire way to kill any engine, but the old S 350 featured in this video managed to keep running until the end. It might not be completely dead yet, but it's definitely in pain. The video from TopSpeedGermany on YouTube shows a thick cloud of smoke emerging from the engine bay, but not before the 1994 Mercedes-Benz S 350 reached 115 mph on the highway. That's the car's top speed, indicating that it still had some of its original 149 horsepower.
However, the top speed was achieved on a downhill stretch after a lengthy acceleration run. Assuming the driver was at full throttle entering the highway, it took 17 seconds to accelerate from 60 kph to 100 kph. The diesel Mercedes was never known for its speed, but this is exceptionally slow. The throttle remained pinned for several minutes until the speedometer finally showed 185 kph (115 mph). The engine was pushed near its maximum RPM for nearly a minute before wisps of smoke began to appear. Keep an eye on the temperature gauge, located to the left of the speedometer. It steadily rose throughout the run, peaking just as the smoke started, prompting the driver to lift off the throttle. This is also when the coolant warning light came on.
The sound quality isn't clear enough to detect specific rattles, but the engine was still running when the driver pulled over after exiting the highway. The smoke appears to be steam, suggesting a possible coolant hose failure. However, given the temperature spike and the intense use leading up to the failure, it's likely that something more serious occurred inside the engine. So, here's a tip: if you're planning a speed run in an old car on an unrestricted highway, it's wise to keep a close eye on the gauges.
