I always thought the 991 shared the same architecture for the dfi engine and pdk design as the 997.2. Of course with some ligthned materials and software improvements, not to mention the thermal management system. But how was the cooling systme improved to be able to remove third rad?

 

It's not completely gone. Some owners in hot locales, Dubai and other Middle East countries, got the third radiator standard. You can also add a third radiator as well to assist with cooling. It may not come standard in most places, but it's still available.