I am including the teardown guide for your unit. This will allow you to open it up and check for dust, etc. 160f is way to hot and is probably the reason the fans are running so hard. I really don't think just dust would cause your problem. If possible determine exactly what is getting hot in there. Since you do movies and looking at the age of the computer I would particularly check the hard drive. Good luck Ralph
[[Device:iMac Intel 17"#deviceGuides]]