High temperature with Yosemite 10.10

Hi,

I have an iMac 21" mid 2011 2.5Ghz, 16GB RAM.

After upgrading to 10.10 Yosemite, I see that the average temperature of CPU when I turn on is 65°C. I open more than two applications at once, Safari (with multiple tabs) and iTunes or Chrome and Illustrator, the temperature rises to 75°C, sometimes up to 78ºC.

Before, with Mavericks, the temperature at power was between 30°C and 38°C. 45ºC Using multiple applications. In the case of doing a render in Premiere or After Effects could reach 60ºC-65ºC, which seemed to me as much.

But now the temperature is much higher than before, and do not dare to make a render for fear of something happening, the rear is very warm.

Anyone know what the problem is? I can not attribute this to anything other than the new OS X. Before had no such drawbacks.

I'm thinking of doing a clean install of Yosemite, perhaps by upgrading from Mavericks and thereby solve the issue ... I do not know this, having to do backup some things bothering me.

What do you recommend? Not if you reinstall on a clean install the Mavericks and bye. Any idea?

Sorry for my english, i hope you understand me

Thanks, Gracias.