There are a few different solutions that I've personally done to fix my MacBook Pro with the same issue.
If you have the Dedicated nVidia Chip I'd strongly suggest installing gfxCardStatus (it's 100% free) and disable the dedicated card altogether. It drains battery, isn't very efficient, emits a lot of heat, and in my case, can cause Kernel panics leading to unexpected shutdowns.
In conjunction to solution 1, I'd suggest also installing Macs Fan Control. A lot of people will say you don't need it and it's true, but Apple usually doesn't ramp the fans up gradually as heat increases, meaning that your MacBook will run hot until it's too hot and the fans ramp up a lot. I'd rather the laptop be barely audible than cook my legs.
I'd highly recommend re-pasting your MacBook Pro as the thermal paste will be dried up by now. In my case, the stock paste from Apple was disgusting; simply too much paste, and now too old.
Previously my MacBook would get up to 76C watching 720p videos in bed (not the best air circulation) with the fans maxed out at 6000RPM. Now, with liquid metal installed, it'll always sit under my custom threshold of 65C when watching videos with just the Intel chip enabled and is dead silent at <2500 RPM. This iFixit guide is what I used in order to do it myself on my 15" MacBook Pro.