Today, we take diesel trucks for granted. They provide huge torque, good fuel economy, and are the solution if towing is your game. But it wasn’t always like this. Go back in time to the late 1970s, and diesel pickups were only just hitting the market. Chevy was the first major American automaker to take a proper swing at a diesel truck, but the result was an engineering disaster that stuck around for just four short years.
If you’re a diehard car enthusiast, you likely already know about this engine, but I just want to write about it today. GM’s first experiment with diesel powered trucks was with an engine that would go down in infamy. Modern Chevy trucks are well known for packing Duramax diesel engines, and prior to that, the company’s pickups relied on trusty Detroit Diesel powerplants, all the way back to 1982. But before that, GM’s efforts hinged on a cursed powerplant known as the Oldsmobile diesel, engine code LF9.
Like I said, you’ve probably heard of this engine before; it starred in the Oldsmobile Delta 88, and stuck around there for a full seven years. It also showed up in a bunch of Buick, Chevy, Cadillac, and Pontiac cars. Few remember it fondly, and even fewer remember that it was actually available in Chevy’s half-ton C-Series pickups from 1978 to 1981. It would prove unreliable, unpopular, and ultimately, forgettable. But why was it so bad?
Slap It Together
To understand the folly of the Oldsmobile V8, and the trucks and cars that featured it, we need to look at its development. In the 1970s, GM was rushing to find a solution for the stringent fuel economy and emissions standards that were hitting automakers hard in the midst of the gas crisis. Diesels looked to offer potentially better fuel economy than big V8 gas engines at the time, and there were different emissions standards for diesels, too. The project got dumped on Oldsmobile’s desk, with the automaker charged with developing a diesel V8 that could power cars and trucks across GM’s range into the next decade.
Oldsmobile engineers decided to start with what they knew, and based their work on the existing Oldsmobile 350 cubic-inch V8. It was this decision that played a role in the failures to come. That’s because a diesel engine typically runs at a far higher compression ratio than a typical gasoline engine. A gas engine might run at somewhere between 8:1 and 12:1, while diesels typically run from 14:1 to 22:1. This is mostly because gas engines are desperately trying to avoid compression ignition of the fuel, while diesel engines rely on that same effect.
The engine’s designers took this into account to some degree, designing a reinforced block for the diesel application. Other changes included hardened camshafts, larger main bearings, and tougher, thicker connecting rods and piston pins.
For all that the engineers did, they didn’t go far enough. The diesel engine’s heads used the same head bolts and 10-bolt pattern as the gas engine. This decision was made to allow the diesel engine and gasoline engine to share some of the same tooling. However, it meant that the head bolts were extremely overstressed in the diesel application. They were more than capable of handling the cylinder pressures of a gasoline engine, but they couldn’t take the additional strain of the high-compression Oldsmobile diesel design, which ran at a lofty 22.5:1. The design really needed more head bolts, and likely stronger ones too, but budget concerns won the day.
As covered by Popular Mechanics, the result was that the engines readily popped head gaskets when the bolts stretched or snapped in the field. This would typically be followed by coolant entering the cylinders, with the additional threat of hydrolocking causing major damage to the engine’s rotating assembly.
An actual running example of an Oldsmobile diesel V8. This is marked as a DX block, suggesting it’s from 1981 or later, though the video states it’s installed in a 1978 model C10. Few of the original engines from 1978-1980 survive as runners as they were just that catastrophically bad.
Another short-sighted move was that the engine was designed without a water separator in the fuel system. It’s sadly not uncommon for diesel fuel to be contaminated with water to some degree, and this was especially the case in the late 1970s. A lot of diesel engines include a system to separate water from the fuel before it reaches components like the injection pump or the engine itself, to avoid corrosion in delicate mechanical parts with tight tolerances. GM’s engineers simply thought this wasn’t important and left it out, which meant corrosion often ended up fouling injection pumps, injectors, and fuel lines in the Oldsmobile engines. Some owners would try and use a product called “dry gas” to try and deal with the water content; often this was a preparation of methanol or isopropyl alcohol that would allow the water to more easily mix with the fuel and burn off. However, in the diesel Olds, this product tended to ruin seals in the pump and cause further problems.
A further issue was that the timing chain responsible for running the injection pump often stretched to the point of failure, too. In any other car, that would be a major headline failure, but it was pretty minor in comparison to the Oldsmobile diesel’s other foibles. Camshafts also tended to wear flat, in part due to a customer base not familiar with diesel-specific oils and the more frequent oil changes needed to deal with soot and contamination.
Hilariously, the problems with the Oldsmobile V8 were so bad that GM couldn’t even sell them in California in 1979 and early 1980. Why? Because the test cars suffered repeated failures and couldn’t complete the state’s emissions tests.
But surely the Oldsmobile V8 offered good performance when it was running, right? Well… not really. The engine was designed more for efficiency than performance. It had neither the most power nor the most torque of all the engines GM offered on the C-series pickup at the time. From its 5.7-liter displacement, the naturally-aspired engine offered 120 horsepower and 220 lb-ft of torque, using indirect injection as was the style at the time.
At best, the Oldsmobile motor would offer slightly better power than the base 4.1-liter inline-six, which only had 105 horsepower and 185 pound-feet of torque in 1978. It was about equal on power with the 4.8-liter inline six, and couldn’t hope to keep up with the gas V8s from the rest of the Chevy range, which topped out with the 7.4-liter big block good for 240 hp and 370 pound-feet in its most powerful configuration.
Where it really shined, though, was in fuel economy. The diesel C10 could get 20 mpg in the city and 28 mpg on the highway—pretty stellar figures for the time. In comparison, the base inline-six would get 16 mpg and 22mpg respectively. You’d get more power out of the big-block V8, but you’d suffer when it came to the bowser. It posted just 12 mpg and 16 mpg respectively.
The diesel was only available on two-wheel-drive models, so it was limited in its appeal. But if you wanted a cheap truck to get around while (comparatively) sipping fuel, it offered a compelling solution. Unfortunately, the reliability wasn’t there to justify the hassle.
Fallout
The obvious result of all these problems was that this demon donk actually spawned multiple lawsuits. One well-known class action was started by Peter and Diane Halferty, customers who had grown increasingly frustrated after two engine replacements and a transmission swap under warranty still netted them a dead car. Ultimately, the FTC got involved, and a major class action ended in GM having to pay up to 80% towards engine replacements for affected customers.
Contemporary coverage by the New York Times in 1983 included quotes from ex-G.M. engineer Darrel R. Sand, who had helped develop the Oldsmobile diesel V8:
In test after test, we had broken crankshafts, broken blocks, leaking head gaskets and fuel pump problems. The diesel couldn’t hold up, it was a hastily converted gasoline engine with a fuel pump designed for heavy trucks.
In the article, Sand claimed that he had told his superiors at GM that the engine should not be put into production in 1977 and 1978. According to the engineer, his warnings fell on deaf ears, as GM badly needed the diesel V8 to help meet increasingly stringent fuel economy standards. Ultimately, Sand would retire from GM in 1980; he alleged that GM had forced him into it as a result of his protestations about the V8.
The Oldsmobile V8 was eventually replaced in the C10, with the 6.2-liter Detroit Diesel V8 taking over for the 1982 model year. It was available on half-ton, 3/4-ton, and 1-ton pickups, unlike the Olds unit. It had a touch more power and torque, starting at 135 hp and 240 lb-ft, and the naturally aspirated engine still relied on indirect injection.
The Detroit Diesel engine had important equipment that the Oldsmobile lacked, like a water separator and a block and fuel line heater to aid starting. The main thing, though, was reliability. Where the Oldsmobile unit couldn’t always be trusted to get you to from Tampa to Atlanta, the Detroit Diesel could take you to Baghdad and back if you were so inclined. That’s because from 1982 to 1993, the same engine played a starring role in the AM General HMMWV, better known as the Humvee.
Despite its reputation, the cursed Oldsmobile diesel nonetheless stuck around until 1985 in some Buick, Cadillac, Chevy, and Pontiac applications. That’s because GM got the design to work after the first few awful years by redesigning the heads and bolts and various other modifications. By 1981, the “DX” version of the Oldsmobile diesel V8 was much improved, and a 4.3-liter diesel V6 was also offered from 1982. And yet, as far as consumers were concerned, the damage had already been done. Having been eliminated from the C10 in 1982, Oldsmobile diesels of both types would cease production entirely after the 1985 model year.
It was an inauspicious start for diesel pickups in the US. Dodge had a false start, too, which is a story for another time. Meanwhile, Ford avoided much of the embarrassment as it held off on launching a diesel pickup of its own until 1983. These days, diesel trucks are stout and capable workhorses of great capability, but on their entry into the US market, they were anything but that.
Image credits: Chevy, GM, Oldsmobile, Always Another Project via Youtube Screenshot
For what it’s worth, I drove a 1979 Olds Delta 88 with the 5.7 diesel from Cleveland to San Francisco. In January 2017.