Putting the sims on the external drive would only make the sims run even more slowly and not solve the heat issue.
Have you done your best with the canned air cleaning?
Example at http://forums.cnet.com/7723-6122_102-569818/getting-ready-to/?tag=contentBody;threadListing
Over the past few months my laptop of almost two years as been acting slow and over heating when I play games on it. The only game I play on it is the Sims 3 with all of it expansions and because of the slowness and over heating I haven't been able to play in months. I have been considering getting a new laptop but a friend told me I could fix the one I have for cheap.
He told me to buy a external hard drive and reformat my laptop. Reinstall windows 7 on it and install all my sim games on the external hard drive. He said this wouldn't make my computer slow and it shouldn't over heat anymore.
I have no idea if this would work and I want to get some opinions on what I should do. Should I just look into getting a new laptop or should I try and fix the one I have currently.