We study the expected X-ray luminosity of stellar merger products several years after merger .
The X-ray emission is assumed to result from magnetic activity .
The extended envelope of the merger product possesses a large convective region and it is expected to rotate fast .
The rotation and convection might give rise to an efficient dynamo operation , therefore we expect strong magnetic activity .
Using well known relations connecting magnetic activity and X-ray luminosity in other types of magnetically active stars , we estimate that the strong X-ray luminosity will start several years after merger , will reach a maximum of L _ { x } \sim 3 \times 10 ^ { 30 } ~ { } erg~ { } s ^ { -1 } , and will slowly decline on a time scale of \sim 100 ~ { } yr .
We predict that X-ray emission from V838 Mon which erupted in 2002 will be detected in 2008 with 20 hours of observation .