Moto G becomes iron Box during voice guided navigation

I have Moto G , bought it happily for great discount and in the beginning was little unhappy because of poor camera but got adjusted. Just I thought is okay. But, I recently have been observing that it has got an issue. When I enable GPS and start GPS navigation app, it says nothing but works flawlessly. But after some time, it gets hot like red. I do not feel that is normal. It makes me uncomfortable to hold it! Is it normal is my question? Are there any other users of Moto G with same issue? Rather I would call it observation. Thanks for relieving me from this feeling.
