Back in the 1990s, Mobil 1 organized an unusual endurance test to highlight the importance of regular maintenance. The subject was a BMW 3 Series E30 with an M20 engine. After a break-in period of just over 1,000 miles on public roads, this 325is spent the next four years in a laboratory. It stayed there literally day and night.
By the time the test wrapped up, the car had done an impressive 1,000,000.5 miles (1,609,344.8 kilometers). The 3 Series ran on Mobil 1’s super unleaded plus gasoline and used the company’s fully synthetic oil. Every 7,500 miles (12,070 km), the inline-six received an oil change per BMW’s recommended service schedule.
The first 50,000 miles (80,467 km) were part of a durability cycle at a steady 55 mph (89 km/h). The remainder simulated highway driving by repeatedly going from 40 to 85 mph (65 to 137 km/h) and back again until the odometer hit one million miles. Throughout the four-year test, Mobil 1 followed BMW’s maintenance requirements to the letter.
At the end, the naturally aspirated 2.5-liter engine was removed and thoroughly inspected. The six-cylinder was found to be in near-perfect condition, showing minimal wear. Most components were still within factory tolerances despite the seven-figure mileage.
Whether the outcome proves the M20’s durability, Mobil 1’s fluids, or a combination of both is up for debate. You could argue that a million miles on a “treadmill” isn’t the same as real-world driving across varied weather and road conditions. Heat cycles also take their toll on engines, but that wasn’t the case here since the car only stopped for maintenance.
Nevertheless, it was an intriguing long-term experiment and an effective marketing effort. It also underscores the value of regular maintenance. Fast-forward to 2025, and the 35-year-old BMW 325is is still going strong, now with a new owner who will hopefully add even more miles to an already well-used car.
