I assume this is about Classic? Here’s another thread about the issue: WOTLK Classic FPS cap no longer working (Fixed, But...) - #16 by Lunameow-kazzak
Enabling v-sync is workaround which caps the FPS to your main monitor’s refresh rate.
If heavy GPU utilization causes your computer to overheat that is worth looking into as it might cause issues in more GPU demanding games than WoW. I tried to run Classic uncapped for while and I didn’t notice GPU getting any hotter compared to other games with similar GPU loads as uncapped WoW.