sounds like a heat sink problem, or it could be the fan is defective thus leading to a low air flow rate, there by causing the CPU to overheat, thats what happened to my PC , the Fan was running slower "infact Very slowly and my CPU keept over heating", if it is the fan then repair should be easy enough, but take it to a registered tech to get it fixed "if you can".
also have you done any DIY since you have got your PS2 ?
it could be some dust on the inside of the PS2, that is causing the heating problem.