United Parcel Service is rolling out a prototype delivery van that gets 40 percent better mileage than its familiar big, brown boxy predecessor.

The twist here is less high tech than you might guess: It’s not a new recipe for electric batteries or some new exotic fuel. Rather, to deliver big fuel savings, UPS put one of its standard package vans on a strict weight loss program.

By replacing aluminum sheet body panels with rugged, lightweight ABS plastic, UPS engineers have lowered fuel consumption by about 40 percent. Using less sheet metal cut the truck’s weight so much that UPS could then opt for a smaller, lighter engine, saving still more weight. All together, the changes have carved off 1,000 pounds, or about 10 percent, from the weight from the original 5-ton truck design, says Dale Spencer, UPS’ director of automotive engineering.

Five of the slim-line trucks are going through a trial-by-fire at a mix of urban, suburban and rural facilities across the country. The design, known as CV-23 among UPS’ engineers, was created in collaboration with diesel engine-provider Isuzu and Wakarusa, Ind.-based Utilimaster, which executed the composite body makeover.

The design team approached the makeover holistically, examining how one change affected others. For example, switching all of the vehicle’s lights — except headlamps — to efficient LEDs further cut demands on the engine. In the final design a 150-horsepower, four-cylinder diesel with a six-speed transmission was able to replace the 200-horsepower power plant used in the older design.

The plastic body panels also offer maintenance savings. Rather than coating them with a layer of brown paint, the composite material is colored all the way through. This saves the weight of paint — which can be 100 pounds or more — but also hides minor scratches and dings. In today’s trucks, if a ding exposes underlying metal, the truck requires a costly trip to the touch-up shop.

And if damage is worse than a ding, the panels are easy to swap out. In the case of a serious dent, current metal-body trucks would need a shop visit, to either patch or replace the damaged body panel. The CV-23 can avoid many of these service calls. Its panels are designed to snap on easily and are light enough to be stored in the garage for a quick makeover…