A sealing device includes an inner race, an outer race capped on and rotatable relatively to the inner race, a rubber oil seal mounted between the inner race and the outer race, a lubricating oil received between the inner race and the outer race, radiation holes formed in the outer race, and a spoiler provided between the inner race and the outer race for causing convection of the lubricating oil to lower the temperature of the lubricating oil upon rotation of the outer race relatively to the inner race.