The early eighties were likely the single most challenging time for car manufacturers ever. In 1980, average oil prices hit a record high of $99 (adjusted) per barrel. Even scarier were the (predictable) predictions that oil was headed to $150, $200, even $500 per barrel. Vehicles were generally much less efficient than today. CAFE requirements were tightening. What’s a manufacturer of The Ultimate Driving Machine to do? Make a Decidedly Modest Driving machine; what else.
In retrospect, the BMW 528e is almost incomprehensible: 121 hp from the legendary M20 six cylinder engine, in a 2.7 liter version at that. That’s almost diesel territory, for back then. Well, BMW didn’t have a diesel (yet) when the new E28 5 Series was being readied for its 1982 introduction. So why not build a gasoline powered diesel, sort of?
In Europe BMW offered a 1.8 L four in the 5 Series, but BMW felt that a four was out of the question for the US. Automatics, AC, and stop-light grunt were all part of that reality. So BMW developed a rather unusual solution, specifically targeted at the US. Although a version of the eta engine was nominally available in Europe too (as the 525e), it was not all that common there.
The eta (Greek for “e” as in efficiency) engine was designed to minimize pumping losses as a result of high manifold vacuum, intrinsic to throttled gasoline engines, especially higher performance ones (Valvetronic and other high tech solutions have substantially mitigated that now). So the eta engine was designed to be rather a lot like the typical lazy American V8 engine of the times: it developed that 121 hp at a very un-BMW like 4,250 rpm, almost exactly the same rpm that diesels develop their maximum power.
The trick was to use a cylinder head with very small ports and valves, and a cam with very low duration. Essentially it was a drastic de-tune one of the most rev-happy and brilliant sports six cylinder engines ever built. Like all engines in a low state of tune, the payoff was a very healthy torque curve. And the efficiency came from the engine requiring relatively large throttle openings, which reduced vacuum and pumping losses.
The EPA numbers were decent, but hardly stellar (1986 MY, adjusted): 18/22 for the 5 speed manual; 16/22 for the automatic. The 535i meanwhile fell into the official guzzler category, with a 15/20 (auto); 14/20 (stick). By 1986, BMW’s new little turbo diesel was available (524 td), and rated at 21/26.
The eta engine was just fine, as long as you had no sporting ambitions whatsoever. It was as if you were given a valet key for one of today’s high performance cars: just when you would expect the engine to really wake up, it fell dead asleep. A bold move for BMW indeed. The reality was that the 5 Series was hugely popular in places like LA, and for the typical first time buyer who was looking more to show off the propeller on the hood more than one under it, it certainly did the trick for the-stop-and go commute.
And the 528e still has a loyal following. These understressed engine seem to run happily for 200-250k miles or more. Everything is old-school Germanic: high quality materials and components, and not that hard to fix. And the ambiance is of course classic BMW: compact, great visibility, terrific seats, good ergonomics, great handling; everything except for the MIA rev band from 4200 to 6500 rpm.
The great irony of the 528e is that by the time it arrived in 1982, oil was already dropping like a full barrel. By 1986, it was down to $29, and gas was flirting with 99 cents a gallon. But BMW stubbornly stuck with the 528e; frankly way too long. After its brilliant E12 530i and 528i predecessors, BMW loyalists were none too thrilled to see the greatest sports sedan in its time be so utterly emasculated. BMW grudgingly started offering the bigger six in 533i and 535i versions, but limited the number available, undoubtedly because of their gas guzzler status.
Frankly, that wasn’t the only thing BMW was slow with at the time. As much as a modern classic the E28 may be now, at the time, it was a mighty conservative upright boxy thing indeed. The E28 was really just a refresh of the E12, and was looking distinctly old fashioned in the mid eighties. Compare this car to the W124 Mercedes that had appeared the year before, or the Audi 5000, and the Taurus and Sable. And BMW kept the E28 going right through 1989, a car that looked very little different from when it first appeared in 1972. BMW; the Ultimate Cash Cow Machine.
I’ve largely neglected the rest of the E28 family for a reason: I’ve got more 5 Series CCs to come, both on the 524td diesel and the sportier 533i/535is. But the 528e’s unique engine is quickly fading from awareness, so it came first. Anyway, it needed a head start: with 0-60 times of over 11 seconds with the automatic, it needs all the help it can get. A current 535 takes half that long, and is rated by the EPA at 17/26. Now that’s progress we can believe in.