1) Light a fire
2) Let the fire go out (or start to go out). Basically, to the point you get the "reignite" prompt in game.
3) Add fuel to the fire and use the prompt to reignite the fire by blowing on it.
4) The fire will never go about the stated temperature. I've seen as low as 60C and as high as 100C and in between. May be higher in some cases but never very high.
5) Keep adding fuel... No change in temperature.
6) The fire will never go up in temperature
See linked video