Equipped with a 6.0L V-8 gasoline engine and GM 6-speed transmission, base models of this Silverado start at $36,440. Our tester came in at $49,629, the lion's share of that premium being the $7,195 Duramax diesel and $1,200 Allison transmission options. Backed up by almost a century’s worth of heavy-duty truck fabrication, would GM’s newest clean diesel drive home ultimate power yet scrubbed emissions when we turned that key? And were the EPA ratings of 16/20 realistic?
Initial Impression: Muscle & refinement
Christine: "Are trucks getting bigger or am I shrinking already? With no running boards on this big boy, that was one big abyss to step up and in – a 32.4-inch range to be exact. Would it be as much of a stretch to drive this big boy comfortably for a week?"
Scott: "It was dark when I got home and the truck had already been delivered. When I pulled into our driveway, my headlights glinted off the massive silver-tipped tailpipe poking out from behind the rear wheel. It reminded me of those big fat plastic bats that little kids use to knock around wiffle balls. I knew pretty much then and there I was going to like the stout Duramax/Allison drivetrain package installed in this truck. I remember how much I liked my plastic wiffle bat, but I ruined that – cracked it wide open smacking a rock – I’d try to be a little easier on this Chev."
Look & feel: Pure pickup, pure power
While Scott wasn’t that fond of the previous generation’s grill and headlight treatment, he thought the new styling gave this truck a more aggressive muscular look. Both of us liked the overall styling—the interior was nicely laid out and intuitive, and each control was easy to understand and find. For a truck intended for hard work, the light tones of the leather interior would not be our first choice for a work-a-billy ride, but the backseat for three and rear cargo storage are testament to this truck's practicality.
Handling-wise, the Silverado proved quite nimble and precise given its large work truck status. However, not loaded, the ride was choppy and stiff. Beware of the shake and shimmy on some roads. In all fairness, the suspension is tuned for a work truck and is really at its best during towing and hauling. Give ‘im a load and the ride smoothes out nicely, so it’s understandable that the ride would be stiff when this big boy is unladen.
This modern 6.6L diesel with high-pressure common rail direct injection delivery system has less of the click and clack—that notorious rattle—inherent in its mechanical fuel system predecessors. The improved engineering in this clean diesel engine reduces that noise further still, thanks to high-precision fuel injectors. The back and front passenger seating and comfort is further improved with Chevrolet’s noise-reducing foam, seals and spray-on damping.
Fuel-ability: Sweet and smooth
Several engineering enhancements were made to the Duramax diesel to meet 2007 clean diesel specifications. A variable geometry turbocharger provides continuous boost, from initial spool-up to its 120,000 rpm ceiling, with virtually no turbo lag. Consistent boost means more efficient combustion and lower emissions. Fuel delivery is metered through a redesigned high pressure (26,000 psi) common rail system featuring high precision 7-hole fuel injectors for thorough fuel atomization while a larger exhaust gas recirculation (EGR) cooler reduces NOx gases prior to the exhaust oxidation catalyst.
GM color-codes the fuel cap green to indicate clean Ultra Low Sulfur Diesel (ULSD) or B5 (5% biodiesel) fuel only. While we fueled up with ULSD, most new clean diesels are also accepting blends of biodiesel. And sure enough, the owner’s manual said: “It is acceptable to use diesel fuel containing up to 5-percent biodiesel (B5), but the final blended fuel must meet the same specification ... and the biodiesel used for making this fuel must meet the latest version of ASTM specification D 6751.” Higher concentrations are not covered by the warranty. And our fuel mileage? 15.7 mpg, mixed hwy/city.
We do feel that manufacturers are being very conservative with their new designs and emission controls. We bet we'll soon see acceptance of higher blends--and sure enough, while we were writing this review, General Motors announced the support of biodiesel blends up to B20. Initially this will be only for fleet trucks, but we can see GM expanding this to all Duramax-equipped vehicles.
The Enviro-meter: No smoke, no fumes
As is the nature of clean diesels, forget the traditional black exhaust cough. After pre-treatment in an upstream oxidizing catalyst, exhaust gas passes through the diesel particulate filter (DPF) where particulate matter (soot) is captured and held in a honeycomb cell structure. To keep the system working optimally, the DPF goes through periodic automatic regeneration. The onboard computer controls fuel injection to allow unburned fuel to enter the filter at measured intervals where it flares off and generates increased temperatures that incinerate the accumulated soot. The resulting expelled exhaust gas has a 93-percent soot reduction and a 50-percent NOx reduction.
Because of the extreme temperature required to burn off accumulated soot in the diesel particulate filter (DPF), the escaping exhaust gas must be cooled. Four slots in the tailpipe terminator provide airflow, and the exiting exhaust gases create a Venturi effect and pull fresh air through the terminator cooling the expelled exhaust, with emissions on par with gasoline engines.
The real beauty of the Allison 1000 six-speed automatic transmission shines when it shifts into overdrive gears 5 and 6. At 0.71:1 and 0.61:1 respectively, this truck goes from low gear power to high gear econo-cruise. At 65 mph in sixth gear, the tach rides at about 1500 RPM. Class-first range selection function allows the driver to optimize shifting conditions when towing. Had we taken this truck on a highway trip, we would have expected 20 mpg plus.