Just for interests sake, try this. Instead of using the cooler, prop the laptop up by placing a book or something under the rear, making sure not to block any vents when doing so. This will allow air to circulate more freely through those vents. I've found that some of the laptop coolers that allow the laptop to lay flat are useless, and the fans usually just blow a bit of air against the laptop case, they don't do anything to aid internal ventilation. As an added bonus, the raised rear makes for a much better keyboard angle, and a nice typing experience.
If you notice a large difference in temps, then look for a cooler that does the same, but a little more stably than just propping it up.