General Motors Figured Out How To Make A Great Diesel Car Engine Just To Kill It Too Soon

Over 46 years ago, General Motors launched its answer to high fuel prices and the need for greater fuel economy. The Oldsmobile diesel V8 was supposed to usher in a new era, but it was such a flop that many believe it damaged the reputation of diesel passenger cars for decades. That’s especially sad because the improved diesel engine that came immediately after did a far better job of delivering the benefits promised by diesel power. 

But then, just when things were getting good, GM gave up. If GM had begun its diesel-car journey with the Oldsmobile 4.3 diesel, things would have almost surely gone very differently for The General. Unfortunately, GM fixed the problems just in time for sales to fall off a cliff, then canceled the whole project, hoping you’d just forget about the whole thing.

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Forever Living In Infamy

It could be argued those old-school diesels shouldn’t have had such a bad reputation. Sure, the Oldsmobile diesel V8 was a blunder, but GM still managed to control the vast majority of the diesel car market and managed to sell hundreds of thousands of diesel cars per year. But as you’re about to read, sales don’t always translate to happy customers.

We’ve written about why the Oldsmobile diesel V8 was such a headache, but if you didn’t read Lewin’s story, I’ll quote a snippet:

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.

The Oldsmobile diesel V8 had a knack for stretching or snapping its head bolts, leading to blown head gaskets at best or hydrolocking from coolant ingestion at worst. If your Oldsmobile diesel V8 didn’t blow its head, it could have also lost its injectors and internals to corrosion since Oldsmobile neglected to add a water separator to ensure your diesel fuel didn’t have water contamination. Yet, if you somehow lucked out on both counts, maybe the timing chain would stretch out.

The Oldsmobile diesel V8 was so infamously unreliable that it wasn’t certified for sale in California. Normally, something like this would happen because of emissions. In this case, it’s because all nine of the Olds diesel-equipped cars failed to complete the state’s emissions testing program. Every test vehicle had engine issues while seven of the vehicles had additional transmission issues on top of their bad engines.

If you’re scratching your head about how engineers could make such a garbage engine, you should know that reportedly, it wasn’t really their fault. As the New York Times reported, Olds diesel engineer Darrel R. Sand tried to blow the whistle and his efforts were allegedly met by getting fired. How bad did things get? That New York Times article from 1983 opens like this:

Peter and Diane Halferty paid $20,000 for a diesel-powered Cadillac Seville in 1979. Within three years, the General Motors Corporation replaced the diesel engine twice under warranty and rebuilt the transmission once, also under warranty. Just after the warranty expired, the third engine burned out and the Halfertys, two land developers in Seattle, were faced with a $4,500 repair bill.

Mr. Halferty, who said he has spent $18,000 keeping his car on the road, finally, in exasperation, put a classified ad in a local paper last year. It read: ”Has your G.M. diesel auto engine failed? Ours has, let’s take action, call Pete…”

In short order, 200 people called the Halfertys and a new activist group was born: Consumers Against General Motors. ”G.M. told us we had an isolated problem, but we knew it was an epidemic,” said Mr. Halferty, who, along with his wife, gave up paid work to organize the relatively well-off group of irate consumers and assist other groups in about 14 states to tackle the nation’s No.1 auto maker.

Other issues with the Olds diesel included failing injectors that fouled the glow plugs, flat tappets that wore too quickly, and leaky Stanadyne injection pumps.

In the end, some 10,000 people across 14 states demanded a uniform redress program from GM while others launched three class-action suits. How did it get this crazy? While the Oldsmobile diesel was notorious from the start, people kept buying them, anyway. General Motors owned the diesel car market in the early 1980s. In 1981, the peak of sales, GM sold 310,000 diesel cars, accounting for 60 percent of the diesel car market.

I wouldn’t fault you for thinking that this is where the story of the Oldsmobile diesel V8 ended. But GM actually managed to evolve this engine into something worth having in a car. General Motors then sold so many diesel cars that Volkswagen’s 2013 numbers were comparatively peanuts.

Giving It Another Shot

Many historical perspectives on GM’s sadder moments in diesel history end after describing how bad the Oldsmobile 5.7-liter diesel was, but General Motors didn’t give up on the project.

As the New York Times wrote in 1983, complaints about the reliability of the Oldsmobile diesel V8 fell sharply in 1981. General Motors had the correct response to the initial disaster by tackling the weaknesses of the Olds diesel. Engineers redesigned the diesel’s heads, used stronger bolts, and changed to a different head gasket material. The injection pumps got new collars and the glow plugs got better, too. These upgraded engines, identified with “350 DX” on their blocks, didn’t suffer from nearly as many failures as the earlier engines.

Here’s a MotorWeek review of an Oldsmobile 98 Regency with this engine and John Davis noted quality improvements and good fuel economy:

However, it could be argued that it came too late. The original engine was on the market for about three calendar years before GM finally released the upgraded version. So, even though the Oldsmobile 5.7-liter diesel V8 was no longer a migraine inducer, buyers started losing interest. In 1982, diesel sales fell by 43 percent, with the New York Times citing the fact that diesel was now more expensive than gasoline, the cars themselves were more expensive, and GM now had a bad reputation.

Yet, General Motors still wasn’t ready to quit yet. In 1982, the firm introduced two more diesel engines. One was the 4.3-liter Oldsmobile diesel V8, which was just the 5.7 with smaller bores, and the 4.3-liter Oldsmobile diesel V6. The former engine was a weak 90 HP unit that sold for just a year in the Oldsmobile Cutlass Salon, Cutlass Supreme, and Cutlass Calais.

The other 4.3 was better but didn’t really get a chance to shine. As Diesel World writes, a common belief is that the Oldsmobile 4.3-liter diesel V6 was probably based on the 4.3-liter Chevrolet V6. Normally, such a notion would be silly, but remember, Oldsmobile did use a gas engine’s architecture to make the 5.7 diesel.

This time, it did appear that GM did learn its lesson. The 4.3-liter Oldsmobile diesel V6 has the same bore and stroke as the 5.7-liter diesel V8 and the two engines even shared many parts, but the V6 diesel’s crankshaft had 30-degree offsets between the crankshaft throws to account for the V6’s firing order. The V6 diesel even used a Stanadyne DB injection pump like its bigger sibling. Autoweek notes that this engine was pretty much a 5.7 with two cylinders chopped off.

Before you get concerned, GM’s basis for the 4.3-liter diesel V6 was the vastly improved 5.7 diesel V8, which meant that the 4.3 was never known for the catastrophic issues that plagued the original 5.7s. Versions of the 4.3-liter diesel V6 would end up in 12 models across the GM portfolio from the Cadillac Fleetwood to the Chevrolet Malibu.

In a vacuum, it seemed the diesel was a great choice, too. Sure, there were only 85 ponies in the stable, but torque was decent at 165 lb-ft. If you equipped a Chevy Caprice Wagon with the 4.3 diesel, Chevy said you’d get up to 33 mpg on the highway under the EPA’s old testing regimen. That was good for an astounding 726 miles of highway range, provided you never exceeded the speed limit.

Oldsmobile said its engine was this efficient because the new diesels had a venturi-shaped pre-chamber design for a cleaner fuel burn. Low blow-by pistons were used to quiet down the engine, the air intake manifolds were aluminum, the engine had an electric fuel pump, and Olds also claimed higher fuel economy thanks in part to roller valve lifters.

How was it on the road? Well, here’s MotorWeek again:

Davis found that the 4.3 diesel had great performance for a diesel and was only slightly slower than an equivalent gasoline car. Ironically, the car was a bit of a pile, but per Davis, the engine was actually flawless. Instead, the car had a near-total electrical failure and when the car did work, the automatic load leveling system basically had a mind of its own.

A Bit Too Late

Davis noted that things weren’t working out for diesel cars by the mid-1980s. The price of diesel fuel rose higher than that of premium gasoline and now that the country had moved on from the Malaise Era, fewer people obsessed about getting super high fuel economy.

But Oldsmobile was still all-in on the diesel thing. Reportedly, it even began work on a wild V5 variant of its diesel.

Autoweek noted that by now, the diesels were getting only eight percent better fuel economy than cars with a significantly cheaper Iron Duke, so there were even fewer reasons to buy in. Then, of course, GM couldn’t escape the reputation it made for itself in the late ’70s. Sales continued to slide and in 1984, stricter emissions meant GM couldn’t sell diesels in California.

General Motors finally threw in the towel on its diesel passenger car program in 1985 and wouldn’t sell a diesel car to Americans again until the Chevy Cruze diesel nearly three decades later.

It’s hard to say what could have happened if General Motors didn’t cancel the project. It seems like GM made a fine diesel engine, but it took far too long for that engine to materialize. Davis said that by 1984, diesel cars accounted for less than four percent of all cars sold in America. 

However, anyone who has been alive long enough knows that cheap gas prices and good times don’t last forever. Europe carved out a niche in America selling diesel cars, eventually emerging as market leaders when diesel caught on again. In 2014, Volkswagen sold 95,823 TDI “Clean Diesel” cars in America, which accounted for a full 23.5 percent of Volkswagen of America’s sales that year. That’s right, nearly a quarter of all VWs sold in America in the early 2010s were diesels.  Then, Dieselgate happened and now diesels have largely faded back to being the propulsion for big trucks and equipment.

I can’t help but wonder what might have happened if GM hadn’t given up for nearly three decades, but I suppose the answer to that question is irrelevant now. The Dieselgate scandal and the shift toward EVs are slowly ensuring diesel remains a technology resigned for big equipment. At the very least, if you want to rock one of these cars today you’re unlikely to pay a lot for one.