My Pi3 setup is in my attic, hot Texas summers. Saw an anomaly message in flightaware about the high temps, it was 85ºC at one point. Not a deal breaker for the Pi3 but not great either. I had it installed in a plastic case than came with the kit and 3 heatsinks were installed. I pulled it out of the case and for the rest of the day just let the board dangle in the attic, it was down to 75ºC at it’s peak and as soon as the sun started to go down it dropped right in line with outside temps degree for degree and was under 70ºC by bed time. 70ºC by the way is the threshold for the temp anomoly message on your user page in flightaware. FYI temps in the attic were around 49ºC so we’re talking ambient plus 30º.
So I order a different case and fan and put that together, reinstalled in the attic, now running ambient plus 5º!! Honestly suprised what a big difference it made, even being back in a case. No controller for the fan, just connected to 5v and Gnd on the GPIO header. That is all. Carry on!
If you care, this is the case - http://amzn.to/2tAa7Dr
And this is the fan upgrade for that case - http://amzn.to/2uLLfs8