630 (1977), 633 (1978-84), 635 (1985-89)

As the logical extension of the exquisite 2800/3.0 CS coupes, the 6 Series brought the new look of the 7 Series to BMW's large two-door grand touring machine. Even more than the earlier coupes, the 6 Series traded tossability for comfort, sophistication and
interior room.
The 3.3- and 3.5-liter straight sixes brought a worthwhile improvement in torque over the 3-liter. As you would expect from a BMW, the single overhead-cam design is as smooth as a turbine. The five-speed manual (an unusual option in a luxury tourer of this size) makes the car noticeably sportier and more responsive than the four-speed automatic.
The interior is full of straight lines, angles and grilles. It also incorporates a "check control" panel that allows a push-button test of the lights and fluid levels. Nice when new, this device often succumbs to electrical gremlins as the car ages. Before buying, be sure to systematically check every electric gizmo on the car; repairs can be very, very expensive.
The exterior design is pure BMW Bauhaus: clean, simple and elegant. The cars changed very little over the model run, with passing years marked mostly by different wheels. The paint quality of original cars was very good; consequently, it takes a superb respray to bring the car up to OE specs. (Most of the cheap 6-Series cars that SCM sees at auction have had crummy repaints which, when combined with the worn upholstery and tired dash vinyl that unloved cars often have, make them scream "Money pit waiting here!" when they cross the block.)
Stay away from the earlier 630-model cars. Their 3.0 engines have a reputation for cracking their cylinder heads if run hot. Even though the 633 and 635 cars were much improved, check the maintenance files for blown head gaskets or worse. A compression test is always a requirement prior to purchase of any BMW 6-cylinder from this period.
These were wildly expensive cars when new, with the 630 CSi sticker priced at $24,325 in 1977, while a Mercedes-Benz V8 450SL cost a mere $21,245. The 530i of the day, with an identical drivetrain, sold for about half the price of the 630. This high price ensured the exclusivity of the big BMW coupe.
A good 6-Series car can be an outstanding value, in terms of quality of car and performance per dollar spent. Stay away from $5,000 cars, as they will cost too much to make right. A good 633 can be had for $8,000 and $11,000 should put you into a near-perfect one. Will they ever be a sought-after collectible? No. Your best bet is to pay slightly too much for a great car, put 20,000 miles on it over a few years while enjoying its impeccable manners and clean lines, then take a small loss and move on. If you buy the right car in the first place, you'll have a grand experience at a bargain basement price.

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