With an experienced team and a lot of data.
Protect your 1985 BMW 635CSi from the unexpected.
In an effort to freshen an aging albeit pretty design, BMW introduced its E24 6-Series to replace the 3.0CS in the U.S. in 1977.
Designed by Paul Bracq, the 6-Series was handsome and stately, but had to meet more stringent safety regulations, and gained a B-pillar that the 3.0CS lacked. Unfortunately, the 6- Series used a low compression head with air injection, exhaust gas recirculation (EGR), and thermal reactors to meet U.S. emissions regulations, which meant the cars were markedly slower than the European models. The EGR and thermal reactors also produced more heat than the 3.0-liter, 176-hp six-cylinder engines could handle, which caused cracked cylinder head and warping.
Beginning in 1980, BMW introduced a Bosch oxygen sensor and a catalytic converter, which solved the car’s heat problems. In 1983, Bosch L-Jetronic injection was switched to Motronic, which was much more efficient. In 1984, the 6-Series received the option of a manual Getrag 5-speed transmission.
In 1985, the engine size was increased to 3.4 liters and the model was renamed the 635CSi. The boost in displacement resulted in 6 more hp and 19 lb-ft of additional torque. A front air dam made the cars look sportier, and more equipment became standard. It was also available as the more luxurious L6.
The most desirable 6-Series was the M6, produced in 1988 and 1989. The car used a 256-hp version of the 635’s engine, and was only available with the 5-speed. The car retained much of the comfort of the standard 6, but became a high-line performer as well.
Neglected E24 6-Series are easy to find, as their well-equipped and sophisticated set-up meant that standard repairs were often expensive. Today these cars are best to be avoided, as they will ultimately cost more in the long run. Earlier cars, due to their EGRs and thermal reactors, are usually last on the list for enthusiasts, while a good M6 is a fun and affordable businessman’s express. The later 3.5-liter cars with 5-speed are also interesting and distinctive transport. As with any older car, be mindful of rust, and check with a mechanic before spending more than you can afford to lose.