You laptop is properly got too much dust in the cooler.
1st purchase some thermal paste (Cooling paste...).
2nd, dissemble you laptop I think yours is also unibody like my Vaio, it's easy to dissemble it.
3rd, take out the fan and the cooler, rust off the dust from the cooler you should use a vacuum cleaner to clean it.
4th, scrape off the old thermal paste from the cooler, cpu and the chipset - graphics card with a credit card and rust of by apply some isopropyl alcohol, after that apply thermal paste to your cpu and chipset.
5th, install your fan and cooler then resemble your laptop. Check your fan is working properly or not.