Getting to know the GM 3.0L six-cylinder Duramax diesel.

Getting to know the GM 3.0L six-cylinder Duramax diesel.

October 22, 2020 11 By Ray Bohacz

An engineering tour de force.

Brand loyalty runs deep in farm country. It matters little if it is the color of a tractor, a seed hybrid, or the badge on a pick-up truck.

For the 2001 model year, GM introduced the first Duramax diesel in its three-quarter and one-ton Chevrolet and GMC pick-up truck line.

That engine was a game-changer. Even the most ardent competitive brand loyalists and corporate board room members around the Motor City agreed. 

It was a clean sheet of paper approach, and nothing was sacrosanct.

There was an obstacle, though. The fast-expanding and profitable half-ton pick-up truck market was devoid of a compression ignition entry… and one worthy of the Duramax name.

It took nineteen years, but the 6.6L V-8 Duramax now has a younger brother, the 2020 inline six-cylinder Duramax 3.0L.

Design overview

The 3.0L Duramax is a completely new design that shares none of its architecture with any other engine in the company’s line-up. Also, it is the first-ever inline-six turbodiesel offered in the full-size GM trucks.

An inline engine provides the perfect balance of the primary and secondary forces that are created by the rotating and reciprocating assemblies over a V-shaped design.

Thus, its smooth operation is devoid of noise, vibration, and harshness (NVH) and is achieved without the complication of balance shafts.

The block and four-valve cylinder head are aluminum. The block enjoys a deep-skirt design, which means that the casting extends below the crankshaft centerline for strength and rigidity.

The rotating assembly consists of a forged steel crankshaft, forged steel connecting rods, and high silicone content hypereutectic pistons with a thick piston crown and reinforced ring land area.

The cylinder head’s DOHC design has the camshafts’ chain driven from the rear of the engine. The crankshaft drive chain runs the high-pressure direct injection fuel pump, which, in turn, operates the camshafts.

A variable pressure oil pump is then driven via a belt by the crankshaft.

Additional engineering features include a variable runner intake manifold, variable geometry single turbocharger, an advanced active engine thermal management system that separates the coolant flow from the block and the cylinder head, and a high-pressure (36,250 psi) common rail direct fuel injection system that can provide up to 10 inject cycles per cylinder firing event.

The 3.0L Duramax boasts an NVH friendly 15.0:1 compression ratio, and a potent 42.8 psi of manifold boost pressure.

All of this and more allow the new engine to deliver 277 horsepower at 3,750 rpm and 460 lb.-ft. of torque a 1,500 rpm. 95% of peak torque is available at just 1,250 rpm and is sustained through 3,000 rpm.  The maximum engine speed is 5,100 rpm. Extremely high for a diesel.

How does it drive?

The Farm Machinery Digest spent a week in a 2020 GMC Denali crew cab (four-wheel-drive) with the Flint, Michigan-made 3.0L Duramax, and companion 10L80 10-speed automatic transmission.

The torque converter in this application is a centrifugal pendulum absorber design that improves NVH while increasing performance and efficiency.

Though I did not get the chance to use it, an exhaust brake is activated when the tow/haul mode of the transmission is selected.

As an engineer with a calibration background, one word sums up the new engine and transmission, magnificent!

It starts as quickly as a gasoline engine and is extremely quiet at idle and, most if not, all driving states.

I did notice a higher degree of diesel clatter during one scenario. It is my opinion that it was probably induced by a series of calibration protocols coming together, and possibly lower than desired cetane fuel.

You can hear the intake manifold runner path change the induction sound during a more aggressive than usual driveaway. It is not offensive and resembles the sound of an old Rochester Quadra-jet sucking air. The truth be told, I liked it!

The 10-speed automatic transmission calibration is perfectly matched to the torque output of the engine. It is always in the proper gear, and it is accomplished imperceptibly. That is the hallmark of calibration excellence.

My only concern about this engine package is my perceived lack of service access. The engine is small and sits low in the frame of a truck with a high body. The turbocharger is easily viewed, but not much more. If you do your own service, you might want to look more closely before writing a check.

There are two reasons for buying a diesel: torque and fuel economy. The 460 lbs.-ft checks that box, but what about fuel mileage? Well, the truck averaged 30.5 mpg for the entire week of regular use and returned an astounding 42.1 mpg on the highway at 65 mph in traffic. So, I guess that box is checked too!

With a cost premium of only $2,495.00 over the gasoline 5.3L V-8, the stunning Duramax 3.0L is going to earn its place to call many farms and ranches home.