The Top Automotive Engineering Failures: Oldsmobile Diesels

As part of our automotive engineering failures series, Popular Mechanics is rounding up the most dismal design failures in automotive history. Today: The Oldsmobile diesel engines of the 1970s and 80s, which frequently suffered gasket failures and hydrolock and soured Americans on small diesel engines for three decades.

Of the myriad engineering failures from the reckless period at the end of the 1970s and the dawn of the '80s, the one with perhaps the longest-reaching effect on consumer preference was the unrelenting awfulness of the Oldsmobile diesels. While European nations and much of the rest of the world are embracing the excellence of modern small diesel engines, the oily film of failure from these hastily engineered lumps lingers on the American palate.

GM's impetus for creating these engines came from the increasingly stringent federal emissions and fuel-economy regulations that began in 1972. In this era before electronic engine controls, the measures automakers took to follow the rules meant that even the brawniest V8 produced barely enough power to pull a big-body car up a hill. The solution, at least to GM bean counters at the time, was to rush a series of diesels to market. Diesels were not subject to the same emissions requirements as gasoline engines, and Mercedes and Peugeot had both been successful selling diesel cars in the U.S., so it was the General's turn. Though the engine was destined for all GM's car divisions, design responsibility fell to Oldsmobile. The first diesel cars began hitting lots in 1978, and clearly, there were problems.

To begin with, Oldsmobile powertrain engineers based the design on the division's well-trod 350-cubic-inch V8. Don't believe the legend that they simply slapped new heads on the standard block. The new block was reinforced and was built of a sturdier cast-iron alloy, but blocks weren't really the problem. Most of the trouble came from the heads and the fuel system.

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Diesel engines operate using a compression-ignition scheme. The ideal gas laws tell us that as a volume of gas is compressed, its temperature goes up, and, in the case of a diesel engine, it's compressed until the diesel fuel in the combustion chamber ignites. This leads to much higher compression ratios and combustion chamber pressures than are present in a gasoline engine. Typically, diesel engines have more and stronger head bolts to compensate for the diesel's higher cylinder pressure. The Oldsmobile diesel, however, maintained the same 10-bolt pattern and head bolts as gasoline engines, so that common production tooling could be used for both the gasoline and diesel engines.


It was a bad problem, but not the only one. One of the critically shortsighted cost-reduction choices was to omit a water separator in the fuel system. During that time period, water-contaminated diesel was quite common, and high-quality diesel systems then and now include a device that removes water from the fuel. This is important because diesel systems are highly susceptible to rust and any other corrosive elements. Without the water separator, corrosion was common in the Olds diesels' injection pumps, fuel lines and injectors, and that caused failed injection pumps and other maladies. Unwitting owners also took a page out of the gasoline engine owner's playbook and dumped anhydrous alcohol (also known as dry gas) into their fuel tanks to alleviate the water problem. Dry gas chemically bonds with water and puts it back into the gasoline solution, which allows it to pass through the engine without issue. But in the Olds diesel, the dry gas also ate the fuel pump seals and other delicate components.

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There were certainly other issues with the engine: a stretchy fuel-pump timing chain, poor dealer service training and a rushed testing schedule, to name a few. Even in good running order they were just plain loud, and belched quite a bit of smoke to provide acceleration that can best be described as glacial. The things only managed 120 hp and 220 lb-ft of torque. Oddly, the V6 variant of the Olds diesel escaped the ills of the V8, having a denser head-bolt pattern and better overall design. It didn't matter, though—the public relations damage was done.

Production of the Olds diesel lasted only from 1978 and 1985, and it caused a class-action lawsuit that saw owners reimbursed for up to 80 percent of the cost of a replacement engine upon failure. The engines were so bad, they spurred legislators in several states to draft early lemon laws. In the long run, Olds diesels also ruined the American consumer's appetite for diesels for 30 years or longer. Only now are diesels tentatively beginning to reenter the U.S. car market in small numbers—and most of those are from German manufacturers.

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