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General Motors Duramax Turbo Diesel Engine Family Guide

Named after German engineer Rudolf Diesel, the compression-ignition motor used to be extremely popular on the Old Continent until the Dieselgate scandal came to light. On the other side of the Atlantic Ocean, diesel powerplants never captured a significant slice of the market.
General Motors Duramax hood badge 10 photos
Photo: General Motors
General Motors Duramax hood badgeGeneral Motors Duramax 2.8-liter turbo diesel (RPO code LWN)General Motors Duramax 2.8-liter turbo diesel (RPO code LWN)General Motors Duramax 3.0-liter turbo diesel (RPO code LM2)General Motors Duramax 3.0-liter turbo diesel (RPO code LM2)General Motors Duramax 6.6-liter turbo diesel (RPO code L5P)General Motors Duramax 6.6-liter turbo diesel (RPO code L5P)General Motors Duramax 6.6-liter turbo diesel (RPO code L5P)General Motors Duramax 6.6-liter turbo diesel (RPO code L5P)
Full-size pickups equipped with diesel engines totaled a little more than 140,000 sales in 2020 over in the United States of America. Last year came to a close with new-light vehicle sales of 14.46 million units according to the National Automobile Dealers Association, which goes to show that compression ignition is a very small player in this part of the world.

As far as the biggest of the Big Three in Detroit is concerned, General Motors currently offers three diesels in the United States. These are the LWN four-cylinder Duramax, LM2 six-cylinder Duramax, and L5P eight-cylinder Duramax. As for the LH7 four-cylinder lump in the Chevrolet Cruze, Equinox, and GMC Terrain, that one had to be discontinued over abysmal sales attributed to the price difference over the gasoline-fed alternatives.

Chevrolet Low Cab Forward workhorses don’t count either because they’re based on the Isuzu Elf, also known as the N Series. To whom it may concern, these commercial vehicles can be had with a four-cylinder turbo diesel that flexes 520 pound-feet (705 Nm) from a displacement of 5.2 liters.

The smallest Duramax available today is the 2.8-liter LWN. General Motors introduced this lump in 2015 for the 2016 Chevrolet Colorado and GMC Canyon mid-size pickups, and be warned that it wasn’t developed by the Detroit-based automaker. Believe it or not, it’s a VM Motori design that was previously used by Fiat Chrysler Automobiles in the Jeep Cherokee, Wrangler, Chrysler Grand Voyager, and badge-engineered Lancia Voyager.

SAE-certified at 181 horsepower at 3,400 revolutions per minute and 369 pound-feet (500 Nm) of torque, the “Baby Duramax” uses a variable-geometry turbocharger for greater efficiency across the RPM band as well as a balance shaft for improved smoothness. The block is made from iron, the cylinder head is aluminum, forged steel is utilized for the crankshaft and connecting rods, and ceramic glow plus reduce heat-up times. Compatible with B20 fuel, which is a blend of 20-percent biodiesel and 80-percent mineral diesel, this engine is rated at 23 miles per gallon (make that 10.2 liters per 100 kilometers) on the combined cycle for the 2021 model year.

General Motors Duramax 3\.0\-liter turbo diesel \(RPO code LM2\)
Photo: General Motors
The Silverado and Sierra rely on the 3.0-liter Duramax, which is a clean-sheet powerplant developed in collaboration with Opel, the German automaker that General Motors owned until 2017. As a brief refresher, Opel and Vauxhall were both purchased by Groupe PSA, the French automaker that now goes by the name of Stellantis due to the 2021 merger with Fiat Chrysler.

A straight-six engine rather than a V6 like the Power Stroke in the Ford F-150, the LM2 boasts 277 horsepower and 460 pound-feet (624 Nm) from 1,500 through 3,000 revolutions per minute. Indeed, it’s just as torquey as the 6.2-liter small block and it needs fewer RPMs to crank out peak torque. Only available with a 10-speed automatic transmission that features a centrifugal pendulum absorber torque converter for reduced vibrations, this fellow is gifted with a durable cast aluminum alloy for the block and head.

Ceramic glow plugs eliminate the need for a block heater until -22 degrees Fahrenheit (-30 degrees Celsius), and customers are further treated to an exhaust brake available in tow-haul mode. An electronically variable intake manifold, no balancing shafts, nodular iron main bearing caps, and a deep-skirt block design also need to be mentioned, along with hypereutectic aluminum pistons, thick piston crowns, and a flywheel-side camshaft drive.

Very smooth and understandably efficient, the first-ever I6 turbo diesel offered in General Motors’ half-ton pickups is available on every 2021 model year Silverado except for the 2WD Regular Cab Long Bed Work Truck. In the case of the Double Cab Standard Bed LT, the Duramax carries a $2,370 premium over the 2.7-liter turbocharged mill known as the L3B.

General Motors Duramax 6\.6\-liter turbo diesel \(RPO code L5P\)
Photo: General Motors
L5P is how the handle of the most Duramax of all Duramax engines. The 6.6-liter powerplant available on heavy- and medium-duty trucks is produced in Ohio by DMAX Ltd., a joint venture between the Big G and Isuzu. The latest and the greatest Duramax of them all traces its roots back to the LB7 introduced 20 years ago in the Chevrolet Kodiak and GMC TopKick.

Starting with a strong foundation, the L5P became available in the 2017 model year Silverado HD and Sierra HD with 445 horsepower and 910 pound-feet (1,234 Nm) on deck. These ratings apply to 2021 models as well, and be warned that GM isn’t sincere about the six-speed automatic tranny.

Here’s a quote from a five-year-old press release: “The proven Allison 1000 six-speed automatic transmission is matched with the new Duramax 6.6L.” If you dig a little deeper into the 2500 HD and 3500 HD, you’ll find no information whatsoever about the Indianapolis-based engineering firm's involvement except for the name. In other words, it’s a General Motors gearbox badged as an Allison for marketing purposes. Peeps who can’t do without a true Allison can get the 4500, 5500, and 6500 trucks, which are available with a power take-off option that enables the user to run a winch, water pump, hydraulic tools, garbage compactor, buckets, and so forth.

When properly equipped for the job, the force-fed V8 diesel enables a maximum tow rating of 36,000 pounds (16,329 kilograms) as long as you get a Regular Cab 2WD with dual real wheels and a gooseneck hitch. The payload tops 6,523 pounds (2,959 kilograms), which is a little short of the 7,442 pounds (3,376 kilograms) offered by the L8T pushrod gasoline V8.
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About the author: Mircea Panait
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After a 1:43 scale model of a Ferrari 250 GTO sparked Mircea's interest for cars when he was a kid, an early internship at Top Gear sealed his career path. He's most interested in muscle cars and American trucks, but he takes a passing interest in quirky kei cars as well.
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