2001 Audi A6 Engine starts to overheat on a hot day in very

On a 90 plus degree day in bumper-to-bumper traffic the temperature gauge starts heading into the hot zone. Luckily the duration of the traffic end before the car really overheats. Never had the problem before. Another Audi owner said that what I experience is a problem that needs to be looked into. I use Audi coolant and it at the proper level. Please advise
Thanks.