1978-1985 Oldsmobile Diesel V8 – an Unsuccessful Endeavor

By the mid-1970s, U.S. automakers were facing a big hurdle with the upcoming government mandated Corporate Average Fuel Economy standards (or C.A.F.E. for short) which began to be enforced for the 1978 model year. C.A.F.E. meant a drastic reduction in engine displacement and car size. The problem was full-size cars were the bread and butter of U.S. automakers. These were profitable cars for GM, it had done a major downsizing to its entire full-size car line-up to both overall size and and engine displacement for the 1977 model year which had been a big success. This was only a short term fix since the CAFE standard for 1978 model year passenger cars of 18 mpg was going to incremental move up year-by-year to 27 mpg by the 1984 year. This required drastic action on GM’s part.

One of the solutions GM had for meeting these ever increasing standards was an engine its Oldsmobile division had developed, the the 5.7 liter (350 cubic-inch) diesel V8. It seemed to be the perfect solution for GM’s dilemma especially since diesel fuel was readily available at most gas stations at the time. Additionally buyers of large cars expected a smooth engine with good low-end torque. Oldsmobile’s 5.7 liter diesel V8 was a smooth powerplant with good low-end torque, but most importantly it was able to obtain around 30 mpg on the highway which would be a big help in increasing the mpg averages of GM’s different car divisions. After-all at that time Mercedes-Benz had been successfully using diesel engines in its new car lineup for many years.

Unfortunately what the Oldsmobile 5.7 liter diesel V8 turned out to be was a public relations disaster for GM. It caused many of GM’s loyal customers to permanently go elsewhere to buy a new car. This engine was plagued with many problems. It suffered from every ailment, from blown head gaskets to overheating in hot weather. The issues were in fact so many that they are too numerous to mention. The root cause of the issues was that the engine was rushed too quickly through its development and testing phases. GM’s customers inadvertently had to suffer through the testing phase until GM could find fixes for these many issues. Had Oldsmobile more throughly tested this engine before production it would have discovered most of the issues and corrected them before production, thereby ensuring a successful product release.

The 5.7 liter diesel was first introduced for the 1978 model year exclusively to GM’s Oldsmobile division and then quickly spread to GM’s other car divisions. This engine would last until the end of the 1985 model year. Cadillac offered this engine in many of its offerings during this time, this engine was one of the reasons why Cadillac lost many loyal buyers during the 1980s and many potential sales.

Even if this diesel engine had been successful, it still had a few drawbacks not related to its reliability. Just like other diesel engines from this time period, it was a noisy engine generating that typical diesel sound you expected hear from a work truck or an 18-wheel truck. However owners of luxury Mercedes diesel cars at the time didn’t seem to mind, since most owners got used to the sound over time. Same was true with Oldsmobile 5.7 liter diesel owners. Another drawback was the cloud of black exhaust smoke it sometimes generated. Additionally like other diesel engines at the time, it wasn’t well suited for geographic areas where very cold winter temperatures were encountered. The solution to this problem was the use of an engine block heater when parking a diesel car overnight in extremely cold temperatures. And just like most diesels at the time the 5.7 liter diesel had slow acceleration. It had only 120 horsepower but a little more respectable 220 lb-ft of torque in its first iteration, for its second and last iteration which was the more reliable iteration of this engine, output dropped to 105 horsepower and 205 lb-ft of torque but it was capable of highway mpg figures in the mid-30s.

The 5.7 liter diesel was based on Oldsmobile’s very successful small block 5.7 liter (350 cubic-inch) gasoline powered V8 engine’s architecture. The 5.7 liter diesel had the same 4.057 inch bore and 3.385 inch stroke as the 5.7 liter gasoline powered V8. This cost saving approach allowed Oldsmobile to save on initial engine development but it also ensured the 5.7 liter diesel would be plagued with problems since it had an ultra high compression ratio of 22.5:1 which was almost 3 times the compression of Oldsmobile’s late-1970s 5.7 liter gasoline powered V8 engine. To GM’s credit it did fix most of the issues that plagued the 5.7 liter diesel and by its last few production years it was a reliable motor. Unfortunately by this time the PR damage could not be undone creating a PR nightmare that has taken GM many years to recover from.

The 5.7 liter wasn’t the only diesel engine Oldsmobile produced, it also offered for the 1979 model year a smaller bore version of the 5.7 liter which had a 3.5 inch cylinder bore, it was the 4.3 liter (260 cubic-inch) diesel V8 and it generated 90 horsepower and 160 lb-ft of torque. And for the 1982-1985 model years Oldsmobile produced a 4.3 liter V6 rated at 85 horsepower and 165 lb-ft of torque which was available in GM’s mid-size rear-wheel drive cars and mid-size front-wheel drive cars.

In hindsight, GM should have had Oldsmobile design a diesel V8 engine from a fresh brand new design rather than converting an existing gasoline engine into a diesel engine. GM also should have done more rigorous and thorough testing of this diesel engine before its release. This approach would have cost more money up front and would have delayed the diesel V8 engine’s release but would have given GM more profits in the end, kept its customers happy, and would have brought new customers to GM. GM did offer very briefly the Oldsmobile 5.7 liter diesel as an option in some of its pickups had it been a reliable engine this could have helped sales in this growing market segment. Instead the Oldsmobile 5.7 liter diesel V8 is now a text book case of how a great company made a colossal mistake.


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