GM’s 3.0-liter Duramax diesel Inline six is powerfully different
Also making its debut at the 2020 Chevrolet Silverado HD event were the new 3.0-liter Duramax-equipped light-duty trucks. The new engine is unique in almost every aspect when compared to Ford’s Power Stroke 3.0-liter engine and Ram’s third-generation EcoDiesel 3.0-liter. First and foremost, the little ’max is an inline-six-cylinder, double-overhead-cam (DOHC) design instead of a V-6, and uses an aluminum block and heads. But what really raised eyebrows was the engine’s drive system, which is located on the rear of the engine and uses chains to drive the camshafts and high-pressure fuel pump, along with a “wet belt” (partially submerged in engine oil) to turn the variable displacement oil pump.
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This likely raises concerns for diesel enthusiasts who are accustomed to gear-driven reliability, but the reasoning behind the unusual layout, according to GM engineer John Barta and Global Chief Engineer Vincenzo Verino, comes down to efficiency and quiet operation. Driving the cams and fuel-injection pump from the rear of the engine, they claim, creates more accurate timing because there is less harmonic distortion at the rear of the crankshaft than there is at the front. This is important, because accurate cam timing and fuel injection results in reduced emissions and increased fuel economy.
Chains are also much quieter than gears, and half-ton customers are generally less tolerant of noise than heavy-duty customers. The chains are designed for the life of the engine, but the oil-pump belt has a useful service life of 150,000 miles, requiring the transmission to be dropped so the belt can be accessed. This sounds complex, but Barta maintains the job will not be a difficult one for a qualified service technician.
To meet ever-tightening diesel-emissions regulations and fuel-economy standards, the engine makes use of several interesting technologies. The fuel-injection system operates at a maximum of 36,250 psi and employs Denso fuel injectors that can pulse up to 10 injections per cylinder event.
Three top dead-center pulses shape the combustion charge for reduced noise, while post injections are used for regeneration purposes. A relatively low 15:1 compression ratio works with an electronically controlled Variable Geometry Turbo (VGT) that creates up to 29 psi of boost pressure and spins up to 175,000 rpm, thanks to a new roller-bearing design. A liquid-to-air intercooler is located front and center on the engine, close to the turbocharger, as it results in a shorter column of air and reduced turbo lag.
Likewise, the emissions equipment is also located close to the engine. As Barta explained, “The Diesel Oxidation Catalyst, or DOC, is close to the turbocharger under the hood so it can stay hot, avoiding the need to inject additional fuel to get it up to optimum temperature.” Downstream of the DOC is the Diesel Exhaust Fluid (DEF) injector, followed by the Diesel Particulate Filter (DPF) and Selective Catalytic Reduction (SCR) unit, which are now combined into a single component GM calls the SCRF. That’s a lot of hot stuff going on in a small area, so GM uses an abundance of reflective tape and three electric fans under the hood to keep temperatures under control.
The engine produces 277 horsepower at 3,750 rpm and 460 lb-ft of torque at 1,500 rpm. Combined with the new 10-speed automatic transmission, 3.0-liter Duramax trucks have a maximum tow rating of 9,300 pounds. We didn’t have an opportunity to tow with the new engine, but we were invited to take it on a driving loop through the mountains around Bend, Oregon. As expected, the engine was quiet, smooth and powerful, but also very fuel efficient. Observed fuel economy was around 21 mpg, but some journalists reported better results when competing for the highest mpg numbers. EPA figures had not been released at press time but should be available by the time you read this.
A frequent contributor to Trailer Life, Chris Hemer is the former technical editor of Trailer Life and MotorHome, and has been an RV and automotive journalist for more than 20 years. An outdoor enthusiast who now makes his home in Portland, Oregon, he enjoys camping, motorcycle riding, mountain biking and hiking.