Hello guys, newbie here at 3d design and such.Anyway,i have completed Blender Guru’s Donut tutorial and i was rendering my donut animation (256 samples, 0.01 noise threshold) and it took me 12 hours to get 300 frames, the problem is CPU was rendering above 90C and hitting spikes of 97-100C, is it going to decrease my CPU lifespan or everything is normal ?
Would depend on the CPU, your CPU might be thermal throttling at that temperature so rendering is going to take longer. Monitor your clock speed and check if it drops at higher temperatures.
Personally i don’t like pushing my CPU above 85c, i like to spend a little bit extra on a decent cooler.
i’ve I7 6820hq processor and nvidia quadro m1000m graphics card, what do you think ??
what is your rendering speed using that gpu?
If it’s an old PC, clean the inside of the case and reapply thermal grease on the CPU
Thermal greases don’t function properly when they’re old.
I don’t think it’s good if the CPU temperature exceeds 85° 
Add…
The nvidia quadrom1000m is unlikely to expect rendering performance. 
Check the specifications for details.
The number of VRAMs and stream processors affects rendering performance.
For every app which uses the computational power of nay PC up to 100% over a long peroid of time.. the cooling system is most essential..
Rule number one: keep your system dust free.
Rule number two : don’t place it where there is not enough air floor.
Rule number three : don’t place it where there it is already “hot”.
Rule number four: The (by the producer) listed maximum temperature of the CPU is meant as the MAXIMUM and not the working temperature.
If one of those fail.. change something !! 
..maybe by an additional or better fan.. may.. be.. (!!)
The maximum operating temperature of that CPU is 100c so you should aim to keep it at or under 90c to 85c under load.
I am guessing that you’re using a laptop so you can’t upgrade the cooling, your best bet is to use a laptop cooling pad. Basically just a mesh stand with built in fans.
it depends on the scene and samples count but it’s doing an acceptable job
By the sounds of it you are using a laptop. Consider using compressed air to clear out the vents of dust build up which can choke airflow. Placing the laptop on a hardsurface to allow good air flow would also help.
Regardless, apart from gaming laptops most laptops sacrifice performance and cooling for aesthetics. They do generally run quite hot.