I get the same issue with my 7140. I was watching a video and the rear of the unit was almost too hot to handle. 

Dell Venue 11 7140, Windows 10 Pro.

Check if the System cooling policy  is set to "Active"

Even with active cooling, as it is heated. It can be controlled to not exceeding 55 ° C, dropping the processor speed to 70% or less, using the power menu or directly in the Windows registry if the option is not available on the menu. It is a problem with the heat dissipation Core M, other brands have handled better than Dell with this model, is a hassle for me too, so that sometimes could not take or support in my legs.