Activist investor Carl Icahn, who holds stakes in two commercial truck manufacturers, is reportedly interested in combining the companies in a bid to trim costs and boost lagging market values.

Speculation about a potential deal involving Navistar International Corp. and Oshkosh Corp. has swirled ever since Icahn disclosed on Oct. 14 that through affiliates he had amassed a 9.8% stake in the Warrenville, Ill.-based maker of trucks, buses, recreational vehicles and engines. Icahn in July reported a 9.51% stake in Oshkosh, Wis.-based Oshkosh.

Though no formal discussions have been held, and it remains far from certain that either company is interested in combining with the other, Icahn, according to Reuters, has been pushing Navistar to consider a deal. The investor in his October regulatory filing said he has had discussions with Navistar management and intends to continue to do so, as well as seek representation on the company's board of directors.

The companies have lost nearly $3 billion in combined market value in the last year as government customers have slowed purchases and timid commercial buyers have been able to demand lower prices on trucks when placing orders.

The logic of a Navistar/Oshkosh tie-up has long been discussed. Oshkosh, which is valued by the market at about $1.78 billion, has been plagued by labor unrest and is more reliant on sales to military and government customers, markets that are expected to continue to slow. Navistar, which has a market capitalization of about $3 billion, meanwhile, has been trying to build its market share in part to spread its cost over a wider base and become more efficient.

Navistar, through its Workhorse International Holding Co. subsidiary, in 2009 acquired the recreational division and other assets of Monaco Coach Corp. for $99 million, but failed in a larger effort to acquire the medium-duty truck business of General Motors Corp. in a deal rumored to be valued at about $500 million.

Combining the two companies would allow them to scale the business and shed excess manufacturing capacity, and potentially get better deals on raw material purchases. Oshkosh could also benefit from using Navistar engines. But a deal is far from certain. Any combination would likely face a cold reception from labor, and one automotive source said that Icahn might be able to generate a better return by shopping each company separately, perhaps to a European or Asian buyer, or by breaking up Oshkosh and selling it piecemeal.