Caterpillar predicted a third-quarter loss.

The company had anticipated reduced earnings in the second half of 1986 but not a loss. Among the reasons for its revised forecast, the company cited lower profit margins on lower than expected sales of large machines and engines, and costs resulting from the 28-day strike in August at the company’s Joliet, Ill., plant. The company said the decline in the value of the dollar should begin to improve prices in North America but probably not before 1987, when it expects to show a profit from operations.