Almost (?) all life runs off chemical reactions that are temperature sensitive and produce heat. In a closed system these reactions stop, they are able to continue (and so life continues) only within a context where the heat is lost.

You can adjust the gradient so as to change the rate of heat loss, you can grow fur, shunt blood flow away from outer surfaces - or the reverse. Humans have clothes and even buildings to do this even more. Say you're losing 10K per hour and producing 5K per hour, if you cut the gradient to 50% you break even and your temperature remains viable indefinitely.

But that only works when you're losing heat. If you can't lose heat, this doesn't help. You will die.