The U.S.-specification E24 6 Series endured a lengthy period of teething problems in the pre-1985 model years. Always down on power compared with its European counterparts, the American version 6er also underwent a sort of personality metamorphosis from sports coupe to luxury coupe and back again with the M6. While it is important to recognize that the E24s officially sold here were never slugs, at the same time enthusiasts should know that the European-specification E24 suffered none of these vagaries. Instead, the Euro version is what one Bimmerhead described to me as "The Truth."
From the moment you see a European-specification 635CSi or M635CSi (the M6 moniker was U.S.-only), it is clear that the car's personality is totally different from US cars--different, but not in a bad way. It's like comparing Meg Ryan with Madonna--we love them both, but for different reasons. Yet Madonna just oozes a more raw allure.
The Euro 635CSi went through two generations, both powered by the similar wonderful high-compression M30 engines. From 1978 to mid-1982, the Euro 635CSi had Bosch L-Jetronic fuel injection with 218 bhp at 5200 rpm and 228 lb-ft torque at 4000 rpm. No catalytic converter was used, and the exhaust system is completely different from anything used in the U.S. A Getrag five-speed manual was used, but it was a close-ratio unit, not an overdrive gearbox as in the U.S. cars. The Euro 635CSi ran a 3.07 limited-slip differential for maximum top speed, which was in excess of 140 mph and depended upon the camshaft one used. It ran 6x14- or 7x14-in. BBS alloy wheels with 205/70-14 tires. A simple front air dam and large black plastic rear spoiler augmented high-speed stability by creating downforce. Recaro seats were used inside, and factory striping outside accented colors like Chamonix white, Henna red, Polaris metallic silver and, of course, black. Buffalo hide leather was optional.
From 06/82 on, the M30 engine power output stayed the same, but TRX tires were used along with the double wishbone control arm front suspension. From 1984 on, a different front air dam appeared, and some cars were fitted with full M Technic body aerodynamics comprised of the air dam, rear spoiler, side skirts, and a lower rear valance panel. The same year, Bosch Motronics appeared as in the U.S. cars, but power remained steady. Driveability improved.
The European-specification M635CSi is, of course, the last word in cool. The brakes are larger, the springs are lower, Bilstein sport shocks are standard, and the massive dohc engine cranks out a lofty 286 bhp at 6500 rpm and 251 lb-ft torque at 4000 rpm. The rest of the drivetrain ratios are the same, but a 7 Series differential was used. No catalytic converter mars the M635CSi, unless it is one of a very small number so equipped at the request of their buyers--early tree huggers running amok as exceptions before becoming the norm.
Nothing is cooler than a Euro E24, and we should consider ourselves fortunate that most of the survivors are probably right here in the U.S. Their desirability is reflected in pricing of well-maintained examples, but be wary of the rats--this is an expensive car to restore. However, if you do restore one, you'll probably ensure yourself a trip to the Good Place in the afterlife. Everyone likes a Euro E24.
E24 Known Problem Areas
The E24 6 Series predates the automotive electronics revolution, which means it has more mechanical systems, and those mechanical systems are pretty much trouble-free. This doesn't mean the cars are trouble-free, but it does mean the problems tend to be straightforward in terms of diagnosis and repair. Here's a quick rundown of some of the more common E24 mechanical issues:
Front-end vibrations tend to result from wheel balancing issues primarily, but do keep tabs on suspension and steering parts, especially the front control arm bushings, aka thrust arm bushings. For performance use, these should be replaced with modified E32 750iL control arm bushings from one of our advertisers who sell them ready to install.
Rear suspension squirreliness can signal the need to replace parts in the rear as well--rear suspension carrier bushings, trailing arm bushings, differential mount and pitman arms.
Brake rotor warpage is sometimes chronic on hard-driven E24s, especially those with automatic transmissions. Try ATE Power Discs first before resorting to cross-drilled front rotors in cases where the problem returns.
Rust tends to attack taillights, floor panels and quarter panels.
European-version M635CSi engines had weak valve springs, which should be replaced with updated units from BMW.
Early U.S.-specification Motronic cars were sometimes given a factory modification to help with engine idle--a small resistor in the electrical harness for the coolant temperature sensor. This resistor fooled the DME into thinking the engine temperature was cooler than it was, thus allowing a wee bit more fuel to smooth out idle. However, it was necessitated by crappy U.S. fuel of the era and can cause problems today. Make sure your tech is aware of it. This and other idle modifications are detailed in the 1987 BMW Engine Campaign Manual, which is available to members of the BMW Car Club of America (www.bmwcca.org) through the Club Librarian.
A no-start condition consisting of no power to the fuel pump is most likely a failed fuel pump relay or main DME relay. No power to the main DME relay can result from a faulty onboard computer control module. Remember that the OBC has a programmable anti-theft function. That's how it works--it cuts power to the main DME relay.