Investor Carl Icahn’s purchase of 9.8 percent of Navistar International shares this month sparked market speculation, especially after buying 9.5 percent of truck maker Oshkosh in June.

Icahn, estimated by Forbes magazine at a net worth of $13 billion, bought both stocks because of undervalued shares. He discussed adding board nominees for consideration at Navistar’s 2012 stockholders’ meeting, but an understanding had not been reached, Icahn stated in Securities and Exchange Commission filings.

On Oct. 17, the commercial truck and bus maker extended its nominating deadline from Oct. 18 to Nov. 15.

Stock market observers also wonder if the 75-year-old New Yorker hopes to merge the two truck makers, but has not publicly indicated plans. Icahn has criticized many corporate boards as ineffective and is a zealous advocate of stockholders active monitoring of investments.

Still, he retreated from attempting to install himself and 10 other nominees to Clorox’s board last month, where with 9.5 percent of shares, Ichan is the largest stockholder.

Icahn leadership includes serving as the long-time chairman of American Railcar Industries and since 2008, the non-executive chairman of Federal-Mogul, an international global automotive supplier.

He described his principal occupation as heading Icahn Capital LP, a wholly owned subsidiary of Icahn Enterprises, a diversified holding company for businesses ranging from real estate to consumer goods.

The Oshkosh production line includes vehicles for commercial, emergency and military uses.