* Coventry Health Care helped fuel gain
* Einhorn outperformed many rivals last month
BOSTON, Sept 4 (Reuters) - Hedge fund manager David Einhorn had plenty to brag about on Tuesday after his Greenlight Capital gained 4.2 percent in August, thanks largely to a double-digit jump in Coventry Health Care's stock price.
Einhorn's Greenlight Capital informed investors early on Tuesday that his Greenlight Capital LP is now up 10.9 percent for the year, said two people familiar with the results, but not authorized to discuss them publicly.
Coventry Health Care, Einhorn's seventh largest position at the end of the second quarter, likely provided the fuel for the fund's gains as the insurer's stock price climbed 28 percent during the last four weeks. Late last month, rival Aetna Inc announced plans to buy Coventry Health Care.
Greenlight Capital, which oversees roughly $8 billion, also benefited from gains in its biggest positions. Technology company Apple, a favorite with many hedge funds and Einhorn's biggest holding, climbed 9 percent in the last four weeks. Seagate Technology, Einhorn's second largest position, rose 4 percent and General Motors, third biggest position, gained 6 percent.
Einhorn performed much better than many rivals during a month when the Bank of America Merrill Lynch's Investable hedge funds index inched up only 0.17 percent.
Many managers are still tallying their results for August but some, like Einhorn, have already sent out their monthly updates.
Daniel Loeb told investors that his Third Point Partners fund gained 1.8 percent to be up 7.9 percent for the year, an investor said. His Third Point Ultra fund climbed 2.7 percent during the month and is up 11.2 percent for the year.
Even though managers like Einhorn and Loeb are still lagging behind the Standard & Poor's 500 year to date gain of 11.8 percent in 2012, their clients are happy to see them post gains for the month. A year ago, in August 2011, many of the world's most prominent hedge fund managers, including Einhorn and Loeb, were caught in August' s sell-off and finished the month in the red.