SO... i have upgraded my pc.
The new PSU seems to gets warmer and warmer causing the cpu to reach 70°C, thing is, is right next to the CPU heatsink.
My question is should i buy a new heatsink, like the vigor monsoon III? or the psu would interfere with the cooling performance?
E8400@3 Ghz (stock)
Coolermaster extreme power plus 600w
ECS 275GTX BLACK
A new case is not an option...
I suspect your overheating is caused by the GPU, not the PSU.
If I'm looking at right card on the ECS site the heatsink dos not exhaust the hot air outside the case which will cause major heat soak.
Check your GPU temps and see what you can do to remove that heat from the case.
I had big problems with rapidly creeping temperatures which I have solved be removing the blank from the expansion slot below the video card (Asus EAH4850) and adding a side exhaust fan above to remove the heat from the case.
Despite the dust issues caused by running the case at negative pressure I have found this config far more capable of cooling. I'm running a Phenom 9750 (OC+Hot) and an ATI 4850 (OC+Hot) with 1 120mm intake and a 120 and 92mm exhaust in a cheap matx case and have not heat problems even in summer at around 30 celcius room temp.
The Coolermaster EPP PSU's aren't great (I have a 550 in the system mentioned) and do run a bit hot and loud but even if your is running hot it should be drawing air from around the CPU and exhausting out the back do should not heat the CPU.
Improve the airflow in to your case adding some intake - outtake fans (or changing with better ones ), if its possible. Use also the air-blower freakykiwi recommended.
What case u have? Maybe u will get a better one in a low price, instead of a large heatsink. NZXT M59 will allow a much better airflow and it will keep the system much cooler. I noticed the "A new case is not an option... " part, but i suggested anyway, as a commonsense and money value option.
It would be your gpu making all the heat. I have 2 8800 gt in sli and my old case would get my cards to 170. I fixed this by getting an Antec 900 case it make a huge difference in my temps all around. My gpu now stays around 130 or so.
Check the cpu voltage in the bios. I just had the same thing happen and it turned out that the (Asrock AliveNF6P-VSTA) bios was setting the cpu voltage at 1.45v instead of the recommended 1.3v. The cpu is on the motherboard's support list and this shouldn't have happened. When I reset the voltage to 1.3v the overheating problem went away.