In a surprise announcement, filtration giant Donaldson Co. late Friday downgraded its 2015 earnings outlook for the third time in six months.

The Bloomington-based maker of filtration equipment for factories, planes, trucks, tractors and construction projects blamed the downgrade on soft engine product sales, weak industrial orders from China and the continued negative impact of a strong U.S. dollar abroad.

Donaldson's preliminary announcement, made after the stock market closed, landed three weeks before the company is to release its fiscal third-quarter earnings. The sudden update couldn't be helped, company officials said.

"The second half of our fiscal year has been disappointing, driven by an unforeseen slowdown in our engine aftermarket distribution channels [and] further weakening in industrial conditions in China," said Donaldson's new CEO, Tod Carpenter.

Chief Financial Officer Jim Shaw added that market demand continued to soften for the large tractors, combines, and construction and mining vehicles for which Donaldson ­typically makes filtration equipment.

Donaldson joins other U.S. manufacturers in wrestling with slower agriculture and mining equipment sales. Companies such as John Deere, U.S. Steel, Cliffs Natural Resources and Magnetation have all scaled back various parts of their businesses in the wake of weak demand or pricing woes. Donaldson also joins such firms as Valspar, Pentair and Polaris in complaining about the effect of the high U.S. dollar.

Donaldson officials on Friday said that negative currency translations involving the sky-high U.S. dollar will nip 5 to 7 percent from total 2015 revenue. On the plus side, Donaldson continues to see growth in "on road" truck filtration products, factory replacement filters and its gas turbine business, Shaw and Carpenter said.

Regardless, Donaldson downgraded its full year sales and profit forecasts.

Full 2015 sales are now expected to fall 4 to 5 percent to between $2.3 billion and $2.4 billion. That's down from February's forecast of $2.4 billion to $2.5 billion. It's also well below Donaldson's November sales forecast of $2.5 billion to $2.6 billion.

Earnings for 2015 are now expected to reach only $1.51 to $1.61 per share, which excludes $10 million in restructuring charges and $4 million in pension costs. The new forecast is down from the prior guidance of $1.65 to $1.85 per share.

Carpenter, Shaw and other company officials announced they will discuss the revisions during a newly scheduled webcast with Wall Street analysts at 9 a.m. Monday. Donaldson will release actual third quarter results on May 21.

Donaldson's stock closed Friday at $37.70, up 33 cents. However, it was falling in aftermarket trading as investors digested Donaldson's revisions. The stock is off its 52-week high of $43.31 a share.