the ps3 fat's get hotter trust me I have had both, and as long as hot air is coming out of the back of your ps3 slim, there is nothing to worry about, the ps3 slim has a better fan, and it does not use the solder which dries up when it get's too hot (as in the ps3 phat).
if you are having serious problems , it may just be a one-off most of us here do not have problems with our ps3 slim's

You need to put the PS3 in a open area. If you put it in a closed off area where it won't get enough air to cool itself, it will overheat and get hot.

Does it like have air to breathe

Remember the video when some guy cooked a pair of steaks on the PS3? That was real!

hmmm i had the same problem one stage, it kept turning off by it self