check the matress tag, if its over 8 its time to replace. lol just kidding.
i think its time to replace the thermal compound/grease/paste cuz most of them dry off after several years like that guy said. or make sure that its not clogged with dust and dirt, cuz dirt is a heat and static magnet.
may i recommend this cooler, its a rosewill for 15 dollarshttp://www.newegg.com/Product/Product.aspx?Item=N82E16835200014