I have an iMac 5k late-2014 with R9 M295x GPU, I'm using the graphic drivers from bootcampdrivers.com, as the default ones don't work with newer games like Forza Horizon 3... However, whenever the game is using much power, the iMac screen goes black, the fan speeds all the way up and after about 10-15 seconds it stops and the windows Login screen appears (no complete shutdown, only sleep mode), Applications and Games are still open but the network connection was gone (disconnected from online matches)... I had a freeze problem with macOS before but a complete formation of the Fusion Drive fixed this... If it isn't caused by the drivers, what could this be? GPU overheating, CPU or RAM not working correctly? GPU reaches about 110° max while playing. Thanks for your help!
By the sounds of it your iMac is overhheating.
A temperature of 110° is too much so your graphics card stops processing for some time in order to prevent any lasting damage to it. As it is only your GPU restarting and throttling, your applications are still open.
As the iMac is an all-in-one, some airflow and heat capacity drawbacks have to be taken.
In order to prevent this from happening you could do the following:
- decrease the graphics settings
- open your iMac and clean the air intakes and outlets to improve ariflow
But remember. The iMac was not designed for gaming on windows, so your experience will never be perfect. Drivers that have been tinkered with might work but should not be considered reliable.