have you got vsync on if so turn that off and cap your frames to a certain level because with the ue4 engine the game and in this case your gpu is trying to keep up with your refresh rate cq fps to what your monitor can handle
this happened to me in adifferent ue4 engine game and my gpu was 87degrees celsius just in the menu!!!!
just to add a note i upgraded my cooling in my case and it didnt do ❤ ❤ ❤ ❤ and then i found out the thing descibed above try it and hopefully it works for you like it did for me