overheaating

this ps3 is a Super Slim cech 4314c never opened and i never received that message from overheating when i turn it on the rsx its always around 70C and the console feels cool by the touch the cpu temp doesnt go higher than 52C but the rsx can go to 89C

To prevent overheating should i replace the PSU [as the original one has metal body, therefore more conducting for heat] to reduce overheating. Also which PSU is the best for replacement.

i have dissembled it and cleaned it and cleaned the psu and the fan even changed the both of them and applied new thermal paste but my rsx still goes to 75°c to 80°c after 1 minute i power it on , have tried also removing it's covers and even added a big cooling fan under it but no luck it still...