At a time when the price of diesel fuel was at a record high, General Motors and other light truck manufacturers were still moving forward with all-new diesel engines for their half-ton pickups - claimed to be ready for 2010. However, as time went on nearly finished diesel powerplants from both GM and Ford were put on the indefinite back burner as economic conditions laid ruins to their business plans.

Although currently "on hold," we still believe the Silverado 1500 with a diesel powerplant could be in the cards for the near future at GM. Pay no attention to the 2500 HD decals on the doors of the Chevrolet Silverado engineering mule in these pictures - this is surely a 1500 test mule. The six lug wheels (instead of eight, like the real 2500 HD) give away that it's actually the 1500 series pickup and the exhaust-cooling Venturi tailpipe out the back is GM's diesel powertrain signature.

Under its hood is GM's revolutionary new dual-overhead cam 4.5-liter Duramax V8. The 4-valve engine was designed with 6 dozen fewer parts than a conventional diesel. Separate intake and exhaust manifolds have been eliminated and integrated directly into the engine. Airflow is reversed, so fresh air enters through the outer portion of the cylinder heads and exhaust gases are dumped inboard into a variable vane turbocharger and EGR cooler that sits in the valley of the 72-degree V8. Removing hardware and rearranging key components reduces the 4.5-L Duramax's footprint compared to conventional V8 diesels with similar displacements, so the 4.5-L Duramax can fit in the same space as GM's 6.2-L small-block gas V8.

GM officially says it expected the 4.5-L Duramax to deliver class-leading horsepower and torque, with ratings in excess of 310 horsepower and 520 pounds-feet of torque. It would also meet stringent 2010 light-duty emissions in all 50 states, using a diesel particulate filter to remove soot and urea selective catalytic reduction to scrub nitrogen oxide. Despite all of the restrictive emissions equipment, GM says this truck should average 25% better fuel economy that its gasser counterpart.

Even though it shares the Duramax name with the heavy-duty 6.6-liter V8 -- which has been engineered and produced in partnership with Isuzu Motors -- the new diesel was 100% designed by GM and will be built without Isuzu's involvement.

Currently, the release of this diesel has been put on hold by GM until market conditions are suitable for its launch.

Spy photos taken July 9th, 2008