In today’s edition of Abandoned History, we once again look back at General Motors’ late ’70s engines. After the disaster that was the V8-6-4 and the subsequent release of the rather flawed HT4100 V8, we’re stepping aside today into diesel. It’s time to take a spin with the discounted cast-iron Oldsmobile oil burner that accompanied troubled gasoline engines at GM dealerships across the country.
Unlike the previous two engines covered in this miniseries, the Oldsmobile diesel was not a Cadillac exclusive. It was rather split across General Motors’ passenger car line in the late 70s and came in three different engine sizes with two cylinder counts. It even found its way into front and rear wheel drive cars.
The diesel story begins like any other, with federal legislation. Emissions had to go down, miles per gallon had to go up, and diesel seemed like a sensible solution. Although nearing its end, GM divisions were still receiving funding to develop their own engines in the late 70s. to implement money-saving tactics.
When Olds designed the 350 (5.7 liter) diesel, someone decided that the best and cheapest solution was to share some parts with the 350 petrol already in production. So they used the same headed bolts. The bolt design and pattern remained unchanged from the gasoline engine, which meant that no new tooling was required. This was a problematic decision as far as diesel engines go, because diesel engines run at much higher compression than gasoline engines (22:5:1 here). The pressure in an oil burner can be three times that of a similar gasoline engine.
That wasn’t the only thing GM neglected to consider, as they also omitted a water separator. In diesel engines, the water separator is part of the fuel filter and is hydrophobic. Water in diesel fuel cannot pass through the filter and is collected at the base of the filter where it drains outside. Drainage prevents corrosion inside the engine.
The general decided that the engine did not need a water separator, as these cost money. This might not have been a huge problem if the United States had been supplied with quality contaminant-free diesel in 1978. But it wasn’t. As the quality of all at that time, the quality of diesel fuel was lacking. Fuel-related issues included the timing chain that operated the fuel injection pump. Simple use caused the chain to stretch. This meant that the pump was a little careless about delivering fuel and did it too late.
All of these components created a perfect storm in the new Oldsmobile diesel engine; developed in haste and on the tight budget mentioned above. A diesel project engineer warned management that the engine was not ready for prime time and was having problems. But General Motors was more concerned with the looming big bad monster that was CAFE. They sent the engineer to collect his things and retire early.
The completed engine was coded LF9 and extended to most of GM’s passenger line. Buick, Cadillac, Chevrolet, Oldsmobile, Pontiac, and GMC all implemented the LF9 350 V8 in 1978. From its 5.7-liter displacement, the engine managed 120 horsepower and 220 lb-ft of torque. The diesel went well in nothing of these vehicles. Keep in mind that design issues were often compounded by GM dealership mechanics who knew next to nothing about diesel engines and weren’t used to tearing them out.
The terrible decision to use gasoline spec head bolts resulted in general overheating, head gasket failures and head bolt failures that sometimes gave up the ghost. The V8’s lack of a water separator meant water lingered in the fuel system. Much of said fuel system was steel, so it rusted from the inside.
Enterprising owners found a solution to the diesel water problem and decided to add anhydrous alcohol (or “dry gas”) to their fuel tanks. Although this absorbed the water, the alcohol reacted badly with the inside of the (already rusty) injection pump. Pieces of the regulator rings in the pump broke off and blocked the fuel lines. Whoops. Said owners made another mistake when they failed to consider that their Cadillac or similar diesel was taking on a different motor oil than the gasoline one they shared a garage with. With the wrong oil, the engine’s crankshaft bearings weren’t long for the world.
General Motors recognized (internally) the problems with the 5.7 and updated it from 1981 with a revised series of engine blocks. This version included a water separator and a revised cam, but the changes came at a cost: less power. After revisions, the engine only developed 105 horsepower and 205 lb-ft of torque.
The modifications made to the 350 did not prevent the wide variety of class action lawsuits filed against GM for their faulty diesel engines. The parties involved wanted GM to publicly acknowledge that its diesels had issues. CARB did not certify the V8 for sale in California in 1979 or 1980: examples shipped to sunny California for testing failed before testing was complete. GM sent nine cars to the West Coast, all of which had major engine problems. Seven of the nine had transmission failures, as the THM200 they used called it.
Oldsmobile developed another version of the V8 for 1979, in the LF7. A 260 cu in (4.3 L) engine, its output was considerably less than that of its bigger sibling. It only pulled 90 horsepower from its displacement and 160 torque. The 4.3 was available for a single model year and was only sold in two Oldsmobile Cutlass models, the Salon and the Supreme.
The problems were widespread enough to attract the attention of the FTC in 1980, when it filed a three-part lawsuit against GM. The FTC cited GM’s diesel engines, current transmission problems and some cam problems in other gasoline V8s. Unfortunately, the FTC bit more than it could chew with the diesel problem. While the sizable administration involved in citing 12,000,000 GM vehicles turned out to be a ton of bricks. In a first, the FTC recommended that the matter be referred to Better Business Bureau volunteers for arbitration.
FTC interference from big names didn’t deter GM from offering the diesel, where it was especially prevalent in Oldsmobile lots. The 350(D) was offered in 19 of 23 Olds models in 1981. That year was the last good year for GM diesels; in 1982, the option was chosen by 43% fewer customers. Along with the widely publicized horrible reliability, fuel prices plummeted in 1982 and made diesel even less attractive.
Still, diesel development continued at Oldsmobile. In 1982 the LT6 made its debut – the program’s first diesel V6. With a displacement of 4.3 liters, it was almost as powerful as the V8 LF7. The LT6 made 85 horsepower and 165 lb-ft of torque and was very slow. Available primarily in 1982 and 1983, it was offered in intermediate sizes like the Buick Regal, Monte Carlo, and Chevrolet Malibu. It was also offered from 1982 to 1984 in the Cutlass Supreme.
Around the same time as LT6, the fourth Oldsmobile diesel appeared. GM had spread its diesel infection to front-wheel-drive vehicles. A transverse version of the LT6, the LT7 diesel was offered in introductory A bodies: Pontiac 6000, Olds Cutlass Ciera, Chevy Celebrity and Buick Century. Available from 1982 to 1985, the LT7 had a displacement of 4.3 liters and offered the same 85 horsepower and 165 torque as the LT6.
LT7 was notable in several ways, primarily for its innovative design. It was the first V6 diesel designed entirely for passenger cars. It was also a very early example of a diesel with an aluminum head. Volkswagen first used the aluminum methodology, and Mercedes-Benz followed GM with its aluminum head diesel engine in 1986. The LT7 proved largely reliable, although head failures did not occur. been unknown given the aluminum construction.
In general, V6 diesel engines were not designed with the same problems as V8 versions. Engineers had more time to prepare and test the engine, and they even used a denser bolt pattern. By the time the more reliable V6 versions arrived, however, the reputational damage had long been done.
Still, the diesel was worth one more attempt, surely. For 1985, a new version of the 4.3 liter V6 appeared. Its scope was limited to new C bodies from Buick, Cadillac and Oldsmobile. Reduced and sad cars used the LS2. The LS2 and LT7 both disappeared in 1985, as General Motors moved away from passenger car diesel engines for a time. The company briefly used Isuzu’s 1.8 diesel in the Chevette and Pontiac 1000 for the truly economy-conscious consumer. They sold 588 and dropped the engine option.
During its three trips, GM sold hundreds of thousands of diesel-equipped cars, and almost none of them were running properly. The debacle did significant damage to the image of diesel engines in the United States, a reputation that arguably never recovered. In the end, GM paid $62 million to 194,000 customers. This figure is consistent with what was published by the Federal Trade Commission, which was not up to the mark. We will come back to the Cadillac V8s in part IV.
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