The ins and outs of why this GM diesel engine is so terrible can be a lot to wrap your head around. That's why a YouTube video from the user OldCarMemories.com was so instrumental in our research. We'll link their video on the comprehensive history of this diabolical engine down below, and we highly recommend you check it out. In truth, the Oldsmobile Diesel line is one GM never intended to rise to such prominence so quickly. Instead, it was the result of rapid changes in emissions and fuel efficiency regulations that took GM entirely off guard.
The creation of the Environmental Protection Agency by President Richard Nixon in 1970 and the subsequent OPEC-fueled petroleum crisis of 1973 prompted new regulations for the Domestic American auto industry that not only put an end to the first muscle car renaissance but led to a dark cloud hovering over full-sized American cars for the next decade at least. New mandatory catalytic converters robbed American engines of their horsepower. There wasn't anything GM could do to stop it.
NHTSA's Corporate Average Fuel Economy (CAFE) standards, had reached as high as 18 miles per gallon by the 1978 model year. That doesn't sound like much to people with modern sensibilities. For some comparison, the light and frugal 1978 Toyota Corolla and Honda Civic from Japan could beat those figures easily. But in American cars, where size is as pivotal to luxury as fine leather, polished wood, and shiny chrome, this was a tough figure to beat.
This put General Motors in an especially interesting quagmire. It may be possible for some of the smaller vehicles in their fleet to reach that federally mandated corporate fuel economy figure, but not to the degree across a range of models that they were now forced to adhere to. As you'd expect, these events sent GM engineers into a frenzy. The only GM engine in the works capable of single-handedly bringing their lineup further into compliance with new regulations came courtesy of Oldsmobile and their 350-cubic inch (5.7-liter) diesel V8.
Dubbed the LF9, it's a common misconception the Oldsmobile Diesel 350 was a compression-fuel conversion of the lauded 350 Chevrolet small block engine. This is inaccurate. Instead, it's a diesel conversion of the Oldsmobile 5.7-liter gasoline V8 architecture native to the brand from the late 1940s through the very early 90s. Has the same bore, stroke, and bottom end as the gas engine it was derived from while being 25 pounds heavier (11.3 kg) due to the larger pistons and larger iron crankshaft, and revised engine heads.
But at least the LF9 did indeed bring the 30-plus MPG fuel economy General Motors expected. Sadly, it came at the cost of the company's dignity once their customers had to live with them. Head gasket leaks, oil pan leaks, corrosion on the fuel injector pumps, water in the fuel, and problems with the Turbo Hydramatic three-speed automatic transmission so often paired with this engine ensured cars unfortunate enough to be equipped with them promptly flooded dealer mechanics across the U.S. and Canada.
In the case of the Cadillac De Ville, Seville, Fleetwood Brougham, and Eldorado, which also received these engines in the early 80s, it was enough to shatter any perception that the brand could still compete with Mercedes-Benz or Bentley in terms of quality. Something they hadn't truly done since the early 1970s, at the very least. Even if the Oldsmobile 350 diesel represented over half of all domestic passenger diesel sales by 1981, the engine was quietly brought out behind the shed and put out of its own misery in 1985.
350 Diesel Olds engine isn't a failure on the level of the Ford Pinto can only be attributed to the fact that, as far as we can tell, it never directly killed anybody. Meanwhile, the Mercedes W116 five-cylinder turbodiesel, made at the same time as the Olds engine, went on to sell in tens of thousands. Many of whom are still driving around today. It just goes to show what happens when an automaker takes their time when designing an engine for once.
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