GM Diesel Engines

In 1938, General Motors had formed the GM Diesel Division which was the ancestor to Detroit Diesel. Being the period of World War II, there was a huge demand for tanks, landing crafts, road building equipment and standby generators. These required the engines to be compact, lightweight, two-cycle products.

The war soon ended but GM Diesel recognized the growing opportunity in the on-highway truck market. The company worked on the development of heavy duty engines to meet the commercial needs and in 1957 it introduced the Series 53 and Series 71 engines for on-highway as well as off-road use.

In the late 1950s and early 1960s GM Diesel began to focus on developing a worldwide network of independent, authorized distributors and dealers to provide parts and service.

In 1965 GM Diesel became Detroit Diesel Engine Division. Five years later, General Motors consolidated the company with the closely allied transmission and gas turbine businesses of the Allison Division to form the Detroit Diesel Allison Division. The Series 149 was also introduced in 1965 to replace Series 110.

Though GM continued to focus on its core business, the engines designed by Detroit while under GM’s control are still very popular and demonstrate the company’s level of engineering ability.

The GM 6.2 liter Detroit Diesel engine was an early effort by the automaker to produce diesel powered trucks and sport utility vehicles. This 6.2 liter diesel engine replaced the 5.7 liter Oldsmobile engine in 1982. The 6.2 was a better engineered engine and was a better alternative to the more thirsty gasoline powered V-8 offerings. The 6.2 was used for Chevrolet, GMC C/K pickups and the Hummer H1.

Introduced in 1982 the 6.2 liter engine was found to be fuel efficient. The horsepower was rated at 130. By 1993, the horsepower was raised to 143. The torque was rated at 240 foot pounds. Torque is the twisting force generated to give the truck of SUV towing power and acceleration. The torque was rated at 257 foot-pounds in 1993. The weight of the engine was 700 lbs.

GM 6.2 liter diesel engine was replaced by 6.5 liter engine in 1993. However, the 6.2 liter diesel is still a favorite among truck restorers as a replacement engine. Vintage Chevy and GMC trucks are often modified by their owners to operate on the 6.2-liter diesel. Many of these engines were also used in older models of Land Rovers. The GM 6.2 liter Diesel engine is still popular due to its availability, easy maintenance and affordable price.

The 6.5 liter diesel engine that replaced the 6.2 liter was not meant to be a power and torque competitor with Ford/International and Dodge/Cummins. It was rather a simply devised workhorse engine that made credible power, achieved decent fuel economy and met emission standards in half-ton trucks. Most 6.5 liter engines were also equipped with a turbo. This engine is still produced for the HMMWV.

There are several options in the GM 6.5 liter diesel engines. The Turbocharged L56 was used in most of the half ton and light duty ¾ ton trucks. The heavy duty ¾ ton and 1 ton trucks used Turbocharged L65 engine. While the L56 is emissions controlled with EGR and catalytic converters, the L65 engine has no EGR or catalytic converter. However, there is a soot trap in L65 engines that is often mistaken for a catalytic converter. Apart from L56 and L65, the other versions of GM 6.5 liter diesel engines include L49 and L57. The L49 and L57 are both naturally aspirated engines. L57 is also listed as a Heavy Duty engine. Other RPO codes include LQM (175 horse power) and LQN (190 horse power).

GM made some changes in the 6.5 liter engines for its light trucks. These were to reduce the emissions and for reliability improvement. In the middle of 1996 General Motors also implemented a redesigned engine cooling system by incorporating twin non bypass blocking thermostats and a 130 GPM water pump. This improved the flow through the block by 70 to 75 percent and also the flow to the radiator by 7 percent.

The technical specifications for the General Motors 6.5 liter diesel engine include:

  • Engine RPO Codes: L49, L56, L65, LQM, LQN
  • Engine Displacement: 6.5 liter / 397 cu in
  • Bore * Stroke: 4.06*3.82 in
  • Block / Head : Cast Iron / Cast Iron
  • Aspiration: Turbo charged. Also available as naturally aspirated.
  • Valvetrain: OHV 2-V
  • Compression: GM Early 21.3:1, GM Late 20.3:1, AMG/GEP Marine 18:1
  • Injection: Indirect
  • Power / Torque (lowest): 180 hp (134 kW) @ 3,400 rpm/ 360 lb feet (488 Nm) @ 1700 rpm
  • Power / Torque (highest): 215 hp (160 kW) @ 3.200 rpm/ 440 lb feet (597 Nm) @ 1800 rpm
  • Maximum RPM : 3400

The fuel system on both the 6.2 and 6.5 diesel engines by General Motors relies on a very basic set up. The 6.2 liter engine is based on a camshaft driven mechanical lift pump that draws fuel from the tank to the injection pump. For the 6.5 liter diesel engine, the lift pump is electrically powered. The injection pump delivers the exact amount of fuel that the injectors require to fire correctly. The fuel system uses indirect injection. For the 1982-1993 engines it was entirely mechanical, quite like that of Ford 6.9 and 7.3 International Harvester IDI. The engines manufactured in and after 1994 have a similar system but use electronically regulated Stanadyne DS4831 series of injection pumps. These are superior to the mechanical DB2831 series found on 1992-1993 6.5 liter engines and the DB2829 found on 6.2 liter ones.

At present GM uses 6.6 liter Diesel engines for trucks from a joint corporation between GM and Isuzu Duramax and the modern engines also have excellent fuel filtration systems to minimize the failures of injection systems. With more efficiency and better power, these diesel engines also cause significantly less pollution and noise. The 6.6 liter engine was initially used in Chevy and GMC trucks and has been used since 2001 for pickups, vans, and medium-duty trucks.

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