Crashing when GPU temperature above 60

[gmls]

Hello

I need some advice on a 2010 21,5" imac that has some stange behavior

I can run the mac for hours doing light work, but when i play a youtube movie or some other harder work it crashes, and when trying to restart it stops halfway true the progress bar. Booting in safe mode keeps working

I installed fan control software and I can see the problem starts when gpu temperatures go above 60°C

I already tried cleaning the fans, reinstalling the OS, installing on external Hd to check it isn't the hd, but the propblem keeps comming back

Is the graphics card broken? when i use the fan control software speeding up te fans to keep the imac cooler it keeps working! but 60° is in my mind not hot enough to crash the imac and when working the graphic cards works perfectly

Strangely when going in the log, the startup freezes on a lot of the following errors:

com.apple.mdworker.single. #number# : service exited due to signal killed: 9 sent by mds (60)

any advice please?

Thank you in advance

 

[burka_tamas]

Video card problen

 

[gmls]

thank you, was thinking in that direction,

Was looking for a replacement but they are hard to find, and when I find one it is on chinese websites