I think the idea of temperature is good, but the implementation needs serious work. In the effort to make all sorts of other things "survivalist" (concussions, broken bones, blood loss, etc.), the temperature mechanic is completely ridiculous. I would not use this as a mechanic for getting sick (as already mentioned, you don't get "colds" just from being cold). Having to find wood in a heavily forested area is also a bit inane. But the temperature drop is still really ridiculous. No one is going to freeze themselves into hypothermia on even a cold September/October night of 40F/3C. My recommendation: Have the "default" temperature be 50 (or 100 and have it go up to 200). Exertion during daylight should increase temperature substantially (probably to the tune of 1-3 per minute), unless it's raining. Rain and night should slowly drop temperature (slower than the current 1 temp per minute, probably), even if sprinting (humans being one of the best mammals at long-distance running, after all). Staying still during the day should tend to normalize your temperature. Going too hot should cause symptoms of heat stroke and heat exhaustion (blurred vision, muscle spasms and cramps (slowed running) eventually leading to fainting). Going too cold should cause shivers and possibly some minor noise making (clattering inventory, chattering teeth and the like) once temperature gets low enough. The benefit is that staying outside when it's dark and rainy will tend to make you cold; running excessively in daylight will tend you towards heat exhaustion. Illness...well the illness mechanic can surely find better uses. Give it to someone who's chronically cold (pneumonia) or give it a chance of manifesting in people who have been injured, with more blood loss tending towards a higher chance of infections and illness. The cold and flu are mostly from human-human and animal-human transmission and are not really related to body temperature. It is a neat, useful mechanic, but if you're going to pretend any semblance of survivalist mechanics is doesn't make much sense in its current iteration.