Gigabyte Z77 DS3H cpu fan not speeding up under heavy load, temps over 95°C

Hello,

My Build is a Z77 DS3H (BIOS F11a) with i5 3570K not OC, boxed cpu fan, GTX 760 and Yosemite 10.10.1. With Mavericks everything was running fine. but now I have a big problem with my boxed CPU fan. In Yosemite it is always running at about 1000 rpm core temps are at 45°C. When I start rendering videos core clocks up from 1.6GHz to 3.6GHz, the cpu fan stays at 1000rpm and the core temp went up to 95°C, then I stopped rendering.
Tried all BIOS settings NORMAL/SILENT/MANUAL/DISABLE. nothing help, always 1000 (+/-20) rpm
While in BIOS the fan rpm are going from 1200 to 2200 depending on core temperature, this seems working. Even when switching on, the fan revs up, but in Yosemite it stays at 1000! ???

Do you have an advice for me,
Don't know what to do, can Yosemite control the fan? Does FakeSMC "kill" then fan rpm?

I'm completely stumped at this point.

Thanks for your help.
Klaus.

I think the bad guy is HWMonitor (If I don't start HWMonitor, while rendering the fan goes up to 2045 rpm and the temp stays at 77 to 80°C.
But as soon as I start HWMonitor, the rpm falls back to 1018.

I'm the only one, with this problem?