the i7-3XXXU series were underclocked by intel for the purpose of saving power while not sacrificing performance. So when you need extra performance it will go boost and start using a lot more power. Unfortunately computers that use the i7-3XXXU (as well as the i5-3XXXU) series CPUs are shoved into Ultrabooks so they have smaller cooling solutions compared to normal sized laptops.
Try getting a Laptop cooler, one with position able fans and move one directly under where the heat is concentrated.
(I have an HP with an i5-3317U, gets hotter than the sun trying to load a simple game.)