FPS drops after playing for a while

[reaperrar 0]

When I first start playing I have really smooth fps. Though it begins to slowly drop over time. After about 15min I have half fps and 30min I have 10 fps or so. What could be causing this and how may I fix it? I've tried playing around with graphics settings, most are on normal. Video Ram is set to highest.

Specs:

Gtx 580

corei7 950 3.07ghz

6gb ram

win7 64bit

EDIT: If I restart the game I return to normal fps and repeat the cycle.

Edited July 24, 2012 by reaperrar

[Genki Dama 49]

why didn't you use the search... there another 59893933983834 million of these threads already

[Owei 0]

->press shift + minus[on numpad]

->type "flush". it wont show you what your typing, but if you typed correctly you'll get a message.

the flush will clear your memory and restarts that cycle you were talking about so you don't have restart the game.

[NightmareP69 1]

why didn't you use the search... there another 59893933983834 million of these threads already

Actully i used search and this is the only thread i found.

So, the same thing happens to me. I start of with a nice 25-40 fps and the it slowly starts droping down. Even goes under 10 fps after a longer while.