What kills an old Mercedes-Benz W140 with an inline-six diesel? Not much, generally speaking. But hammering one down the Autobahn at full throttle for several minutes certainly doesn't help. Ignoring a rising temperature gauge is also a great way to kill any engine, but to the credit of the old S 350 featured in this video, it was still running at the end. Heck, it may not even be truly dead.
It's definitely hurting, though. The end of this clip from TopSpeedGermany on YouTube shows an unhealthy cloud billowing from the engine bay, but not before it powered a 1994 Mercedes-Benz S 350 to 115 mph on the high-speed highway. That's the car's top speed, so it must have at least some of its original 149 horsepower still in play. However, the top speed comes on a downhill stretch after a very long acceleration run. Provided the driver is indeed at full throttle entering the highway, we calculate 17 seconds accelerating to 100 kph ... starting from 60. The diesel Merc was never a speed demon, but that's exceedingly slow.
As far as we can tell, the throttle stays pinned for several minutes until we finally see 185 kph (115 mph) on the speedo. The engine is held near maximum RPM for nearly a minute when whisps of smoke start appearing. Keep an eye on the temperature gauge, located left of the speedometer. It rises steadily throughout the run, maxing out just as the smoke show starts, at which point the driver lifts. This is also when we see the coolant warning light illuminate on the dash.
The sound quality isn't good enough to listen for specific rattles, but the engine is still running when the driver pulls over after exiting the highway. And the smoke we see looks like steam, so the failure could be something as simple as a busted coolant hose. However, seeing the temperature spike and the hard use leading up to the failure, we suspect something more dire happened inside the mill.
So here's a top tip. If you're setting out for a speed run in an old car on an unrestricted highway, it's probably a good idea to keep an eye on the gauges.
