MILFORD, MI – For the first time since 2002, General Motors Corp. will offer a diesel engine with its '06 Chevrolet Express and GMC Savana G2500/G3500 fullsize vans.

Targeting commercial customers, GM expects about 15,000 units to be ordered annually with its Duramax 6.6L turbodiesel engine.

Chevrolet Express

Considering gas prices average more than $2 per gallon in the U.S., GM's decision to offer more efficient diesel engines is timely. It also is a strategic move against competitor Ford Motor Co., which is the only provider of a large diesel engine for fullsize vans with its Powerstroke 235-hp 6L V-8 mill. DaimlerChrysler AG's Sprinter van is equipped with a 154-hp 2.7L inline 5-cyl. turbodiesel engine.

“Diesels tend to provide a 20% improvement in fuel economy,” Jim Weisbeski, vehicle performance manager, tells Ward's. “And they're great for idling, if you have an application where you do a lot of idling or low-speed driving. They usually require less maintenance, and they tend to last longer than a gas (engine) does. So in the commercial segment, all those things are important to our customers.”

Upgrades were made to the Duramax and the Express/Savana G2500 and G3500 series models, which often are used for delivery purposes, school buses, airport shuttles and ambulances.

The engine improvements include: cylinder-block casting and machining changes, revised piston design for a lower compression ratio, reduced cylinder-firing pressure, higher-pressure fuel pump, fuel rails and distribution lines, all-new fuel injectors and an improved variable-geometry turbocharger.

The Duramax beats the Powerstroke offered with Ford's E-Series van in critical specification categories. It delivers 250 hp and 460 lb.-ft. of torque (624 Nm) vs. the Powerstroke's 235 hp and 440 lb.-ft. (597 Nm). The GM and Ford vans each have towing capacities of 10,000 lbs. (4,534 kg).

During a recent test drive here at GM's Proving Grounds, the Duramax was noticeably quieter while idling and coasting, and stronger while ascending steep grades. It is teamed with GM's Hydra-Matic 4L85-E electronically controlled 4-speed automatic transmission.

The '06 Savana and Express G2500/G3500 models receive upgrades, too, including a revised front floor panel, underbody heat shield and new interior engine cover. There also is an optional fuel-operated heater (standard in Canada) to quickly increase the vehicle's interior temperature in cold climates. Because diesel engines run so efficiently, they produce far less heat than gas powerplants to warm the vehicle's cabin. The fuel-operated heater solves that problem by using diesel fuel to produce warmth.

The Duramax also is offered, with a different transmission capable of handling more torque, on the Chevrolet Silverado and GMC Sierra pickups and GM's medium-duty commercial trucks.

“But because we're putting the engine into the van, it's a lot tighter package around it,” Weisbeski says. “We have to modify things like thermostat housing, turbocharger routings, all sorts of electrical connectors, engine mounts. But the base engine itself is common. We're taking advantage of an engine we've been offering in other applications. It's obviously highly refined at this point.”

To cut repair and maintenance costs, GM moved some components, such as the fuel filter, to more accessible positions.