Oldsmobile Diesel V6 engine

Oldsmobile developed three diesel engines for the 1980s: two V8s and a 263 CID (4.3 L) V6. It was based on the Olds 350 V8 with a 4.057 in (103.0 mm) bore and 3.385 in (86.0 mm) stroke.

The history of passenger-car diesel engines at General Motors has been checkered. In the 1970s, the company was unable to power its large cars and trucks with their emissions-strangled engines. Like many other companies, GM turned to diesel power, directing the Oldsmobile division to develop one V6 and two V8 to be shared with all divisions.

Oldsmobile's diesels, the 5.7 L LF9 and 4.3 L LF7 V8s and the 4.3 L V6, were notoriously unreliable. Oldsmobile engineers claimed that management forced them to hold to a time line that didn't allow for sufficient testing. Although over one million were sold from 1978–1985, the failure rate of early GM diesel engines ruined the reputation of diesel engines in general in the United States market. Eventually, a class action lawsuit resulted in an arbitration system under the supervision of the Federal Trade Commission where consumers could claim 80% of the original cost of the engine in the event of a failure.

The primary problem with GM's diesel engines of the 1970s was their design - weakness in the head design and head bolts, which were not able to withstand the higher cylinder pressures and temperatures of diesel use. This design weakness combined with poor diesel fuel quality in the 80's led to catastrophic failure of pistons, cylinder heads, and even cylinder walls. Reinforced truck diesel engines, from GM and other companies, did not have these problems. Today, GM uses diesel engines from DMAX (for trucks) and Isuzu (for non-US cars) but does not offer a diesel engine in any of their North American passenger cars.

Oldsmobile Diesel problems

Head bolts

GM used "torque to yield", commonly known as "stretch" or "angle torque", head bolts. This allowed the bolt pattern to remain the same as the gas powered counterpart with an increase in clamping load when compared to standard head bolts. A total of 10 bolts per head were used. Four per cylinder with the center three pairs shared. This permitted the use of the same tooling and reduced setup costs. This design did not provide adequate clamping force under the severe conditions these engines were subjected to. Overheating or excessive cylinder pressure can breach the seal of the head gasket and in severe cases break the bolts.

High strength aftermarket head bolt sets are now available to make the engine more reliable in this area.

Pump timing

The Stanadyne injection pump was chain-driven. With normal use, the chain stretches and the pump delivers fuel too late. The pump timing could be adjusted to return to normal operation.

Water in fuel

Arguably a major portion of the real problem would have been quite simple to avoid. A water separator was not part of the fuel system on these engines. Water-contaminated diesel fuel was quite common.

Water will rust the steel internals of the fuel system. Rust will damage the precision parts in diesel fuel injection pumps and high pressure diesel injectors causing erratic operation. Injecting fuel too much prior to TDC on the compression stroke will cause pressure conditions similar to pre-ignition/detonation in gasoline engines. Water in varying amounts will also be injected with the fuel charge. Any rust in the steel fuel lines, fuel filter, pump etc can damage replacement parts and continue to cause injection cycles out of time.

Consumer-created fuel problems

Water in gasoline can be dealt with by adding anhydrous alcohol [drygas] to the fuel. This does not work with diesel fuel. Consumers, sometimes unaquainted with this fact, used drygas in their diesels to eliminate water. Alcohol accelerates wear of the governor flex rings inside the early Stanadyne DB injection pumps. These pumps include an ignition advance mechanism based on pump housing fuel pressure. The housing pressure is affected by fuel return flow. Pieces of a damaged governor flex ring lodged in the fuel return check ball assembly. The sometimes intermittently blocked return line combined with a damaged governor caused erratic ignition timing. The flex ring governor was replaced, by Stanadyne in 1985, with a much improved Elastomer Insert Drive Governor Assembly commonly referred to as an EID. The EID is a service replacement part that eliminates the disintegrating flex ring.

The above mix of conditions originating with water in the fuel can combine to create extreme cylinder pressures far exceeding those foreseen by GM engineers damaging the head gasket and sometimes breaking head bolts.

A head gasket leak effectively quenches ignition in the affected cylinder. This allows unburnt fuel and coolant to leak into the crankcase thinning the lubricating oil. It also combines with combustion byproducts to make mild acids that will attack the copper/babbitt bearings and aluminum pistons. A head gasket failure can be particularly damaging in a diesel. A diesel engine has effectively zero piston to head clearance at TDC on the compression stroke. The introduction of coolant into the cylinders can cause hydrolock. Hydrolock typically results in bent/broken crankshafts, pulled threads on main bolts, and bent connecting rods, effectively destroying an engine.

Because the various failures these engines encountered were causally interrelated, and dealership technicians were unfamiliar at best with passenger car diesel engines, recurrent failures were possible because only the most obvious symptoms of trouble were addressed. The "one use only" head bolts were commonly re-used and symptoms in other interrelated systems ignored. Thus, cars could suffer multiple head gasket/head bolt failures from re-use of head bolts or a damaged injection system.

The Oldsmobile Diesel V6 engines were produced on different tooling than their V8 counterparts. They received a head bolt pattern that is arguably a superior design capable of withstanding more abuse.

LT6

The LT6 was a very rare diesel engine produced from 1982-1984. Power was rated at 85 bhp @ 3600 rpm and 165 lb. ft. torque @ 1600 rpm

Applications:

• 1982–1984 Oldsmobile Cutlass Supreme, Supreme Brougham, Calais
• 1982–1984 Buick Regal

LT7

The LT7 was a transversely-mounted diesel engine produced from 1982-1985. Power was rated at 85 bhp @ 3600 rpm and 165 lb. ft. torque @ 1600 rpm

Applications:

• 1982–1985 Oldsmobile Cutlass Ciera and Supreme
• 1982–1985 Oldsmobile 98 Regency
• 1985 (Listed in options 1982–1985) Chevrolet Celebrity
• 1982–1985 Buick Century

LS2

The LS2 was a front wheel drive version produced for 1985 only.

Applications:

• 1985 only: Oldsmobile 98, Buick Park Avenue, Cadillac DeVille

See also

• List of GM engines

References

• "Ghosts of Diesels Past: Failed cars from 20 years ago still haunt GM, U.S. market". AutoWeek. http://www.autoweek.com/apps/pbcs.dll/article?AID=/20050513/FREE/505130704. Retrieved May 13, 2005. 
• Olds 350 Diesel Tech