Truck makers, having embraced the idea that less is more, are narrowing the engine choices for their vehicles. The move started four years ago, and it has accelerated in recent months. It’s intended to help manufacturers lower production costs and keep a lid on retail costs while optimizing the performance of selected components.

Volvo took the first steps in this direction in 1997 when it stopped offering Caterpillar power. Late last year, the company signed an exclusive supplier agreement with Cummins and dropped Detroit Diesel. Cummins is also the exclusive outside engine vendor to Mack.

Officials of Paccar, parent company of Kenworth and Peterbilt, in February made Cummins the company’s default engine and indicated that ties to Detroit Diesel would be severed by mid-summer. Freightliner buyers can still spec engines from Cat and Cummins, as well as Freightliner’s sister companies, Detroit and Mercedes-Benz, but it appears that menu will shrink.

What’s driving these alliances? Corporate mergers, emissions standards and market conditions – major issues for the manufacturers, but of little concern to buyers, many of whom have strong loyalties to truck brands and engine brands.

Paccar, parent of Kenworth and Peterbilt, made Cummins the company’s default engine, giving Caterpillar a secondary status. Paccar officials have also indicated that ties to Detroit Diesel would be cut this summer.

Dan Meyers, owner of Three-D Transport in West Unity, Ohio, runs 20 Kenworths that pull covered wagons across the Rust Belt. All but two of his trucks are Detroit-powered. But that mix is going to change, partly because of a good working relationship he’s established with his Kenworth dealer. “Any piece of equipment is only as good as the service you can get for it,” he says. “There tends to be more maintenance issues on trucks than engines. If it were the other way around, I might be inclined to stay with the engine instead of the chassis.”