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5.7L Oldsmobile Diesel

350 Olds Diesel History

 

 

 

 

 

Face it, when the claim that "older engines gave diesel a bad reputation" is made, the 350 Olds comes to mind. Oldsmobile designed and produced the 5.7L, or 350 Olds in response to the oil crisis of the late 70's. First appearing in 1978, the 350 cubic inches diesel promised the creature comforts of a large, luxury car with the fuel mileage of a compact. Officially named the LF9 diesel, the Olds was offered in Chevrolet, Buick, Pontiac, Oldsmobile, and Cadillac cars, as well as light duty Chevrolet and GMC pickups. Overall, the engine proved unreliable and problematic, and unforunate blow for General Motors. The engine was removed from production altogether in 1985, despite majority of the engine's inherent flaws being addressed. Unfortunately, the 350 Olds would haunt GM for years to come as their tarnished reputation in the diesel marketplace would not be, arguably, repaired until more than a decade later.

5.7L Olds Diesel Specs

Manufacturer:

Oldsmobile

Years Built:

1978-1985

Applications:

Chevrolet, Buick, Pontiac, Oldsmobile, & Cadillac cars. GMC & Chevy light duty trucks.

Configuration:

V-8

Displacement:

350 cubic inches, 5.7 liters.

Compression:

22.5:1

Bore:

4.057 inches

Stroke:

3.385 inches

Injection:

indirect injection (IDI)

Aspiration:

naturally aspirated, non-turbo

Horsepower:

125 HP @ 3,600 RPM

Torque:

225 lb-ft. @ 1,800 RPM

 

There is an enormous misconception that the 350 Olds is based on GM's 350 gas engine. While they share similar architectural dimensions, this is a rumor. Not only would such a design be engineering suicide, but the gas engine would never live up to the cylinder pressures created by the 22.5 : 1 compression diesel. In fact, GM's official statement regarding these rumors was that "All of the major parts: block, crankshaft, rods, pistons, and lifters have been strengthened to handle the higher compression ratio." The rumor that the engines are related likely stems from a combination of the following:
• Because of the engine's identical bore and stroke, the Olds diesel could be manufactured using pre-existing tooling.
• Not only is it easy to assume the 350 diesel is based on the 350 gas engine, but owners and outsiders alike needed to place the engine's problems on something.
Regardless, the 350 Olds was capable of up to 30 miles per gallon in the right car and with the right driver. GM continuously tried to sell buyers on its Olds diesel by identifying it with "prestige" and "status". Unfortunately, by the time most of the kinks were worked out, their customers had fled.

Common 350 Olds Diesel Problems

• Torque to yield (TTY) head bolts provide poor mounting of the cylinder heads. As a result, head gaskets can wear & fail. Head bolts were even known to sheer under the extreme cylinder pressures (the Olds diesel had a very high compression ratio, which didn't help).

• The fuel system lacks a fuel-water seperator. Any water that enters the injection pump can cause parts to corrode & fail. This can result in extensive engine damage.

• Main bolts were too short, often resulting in bottom end failure & crankshaft damage. Crankshafts were not dynamically balanced, further contributing to crankshaft failures.

• GM was in a rush to offer their diesel and be the automaker to "pioneer" the industry. As a result, production of the engine blocks for the 5.7L Olds was rushed. After casting, the "green" (green is a term used to describe a casting that has not had proper time to cure) engine blocks were rushed to assembly before the internal stresses could be relieved. This caused problems with the engines once they were run, as the heat cycles caused engine blocks to flex, often causing misalignment of the main bores. Misaligned main bores contributed to the common crankshaft failures.