I recently added a fan to my case at the rear position in order to blow hot air out of my case. Before I added this fan, I did not have any case fans, so this is the only one I have. Well, prior to adding this fan, I would have idle cpu temperatures of around 32-33c, and now they are up to around 35-36c. Why would this happen? Under load, my temperatures are a little better with the new fan, with my peak temperatures in games reaching around 54c. Before, it would be right below 60c. Does it make sense for my idle cpu temp to be higher with a single rear fan? I have a Pentium E5300, Radeon 4850, and 2GB of ram if it makes a difference. The only other fans I have besides the case fan are the cpu fan, gpu fan, and the power supply fan I believe.
I'm surprised your case didnt have a rear fan to begin with Add an intake fan to bring fresh cool air into the case as well, either front mounted or side panel, your rear fan will push hot air out, but you need a reasonable supply coming into the case too, I have 16 fans in total, but I may have a problem hehe
hope this helps,
Maybe that you have too much negative pressure? If your psu was part of your cooling system before, it could of been better if you made your rear exhaust fan intake, if it does improve, then probably you need a intake fan