Mercedes 420
Reliability, running costs, and MOT data across 2 years from 169 real MOT tests.
Avg Pass Rate
76%
Total Tests
169
Best Year
1991 (77%)
Years Covered
2
How reliable is the Mercedes 420?
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About the Mercedes 420
The Mercedes 420 has been tested 169 times in 2024 MOT data across 2 model years (1990 to 1991), with an average pass rate of 76%. That's 6 points below the national average of 82%, so check the year-by-year data carefully before buying. Available as petrol.
Best and Worst Years
The 1991 model is the most reliable with a 77% pass rate from 44 tests. The 1990 model has the lowest at 74%. With just a 3 point spread, the 420 is consistently reliable regardless of year.
Mileage Across Years
The oldest model in our data (1990) averages 131,208 miles, while the newest (1991) averages 131,577 miles. Older models have covered serious mileage, so suspension and drivetrain wear are worth checking.
Compared to the Mercedes brand average of 87%, the 420 is 11 points lower, placing it among the less reliable Mercedes models.
Click any year in the table above to see detailed running costs, individual reliability data, and comparisons with similar cars.