hashrate decrease

[ses7404]

I've 4 machines mining scrypt on GPU. Im every machine BFGminer at startup has great performance with really high hashrate. Hashrate slightly decrease passing hours till it stabilize at a really lower hashrate compared to startup.
Could it be normal behaviour?

Thanks

[vpasic]

which gpu-s?
what hashrate the end up mining?

[ses7404]

mining with radeon hd 6670, 7850 and 7850 oc

7850 starts at 700kh/s then slowly decrease and after some hours is at 150-160kh/s

[vpasic]

are you watching temperature of your card?
what about other 2 gpus?
7850 should give you around 350kh.
can you try with cgminer 3.7.0 and add this in to your command:

-I 17 -w 256 --thread-concurrency 8192