My i5-3450 is hitting 105c all the time, and I've realized this a bit too late. Is it because of the thermal paste I chose (I'm a fool for not using Arctic Silver) or did I seat the stock cooler wrong?
PLEASE make sure you've put the heatsink on properly. It might feel tight but its probably not. If it comes with screws then turn the screws all the way in! Thermal paste is probably NOT the culprit. Most brands of thermal pastes use the same stuff anyways. (Silicone) Try to tighten the heatsink on the CPU if that doesn't work clean this paste off the CPU and heatsink then just get a artic cooler rev 2 cpu heatsink. Its better than the stock heatsink that comes with intel and it comes pre-applied with artic cooling paste.
clean away the paste with a damp wet cloth (do it thoroughly and gently, make sure no excess water is left on the cpu, dry it after you run the cloth over it immediately) do the same for the heatsink. Then apply a small amount of thermal paste on the CPU (Pea sized. like ( ) then put the heatsink on tightly. Don't spread the compound the heatsink does that for you!