I upgraded from pentium g4560 to i5 6500 and all fans are runing at full speed but the temeratures are normal. I tried to change it in bios but it doesnt help, than i switched back to pentium and fans were runing fine. Is there something wrong with the cpu? Motherboard i use is msi b250 pc mate.
I suspect that, in the upgrade process, your BIOS was Reset. I also suspect that your fans MAY all be of the 3-pin design. I suggest that you re-install the new CPU, then go into BIOS Setup for the four SYS_FAN headers. You need to do this for all case fan headers you are using. See your mobo manual, p. 62. Check two items and set:
At Upper left, IF your fans are 3-pin, set to DC. IF they are 4-pin, set to PWM
Near bottom right, choose the option All Set Default.
Back out using Esc and be sure to SAVE and EXIT. That may get them under control.