On Thu, 18 Jul 2019 16:42:24 +1200, Peter Reutemann quoted:
'So I decided to follow the lead of Redditor u/CarbyCarberson and put a fan in the top cover. [...] After installing the fan, I booted the Pi and ran "stress --cpu 4" and let it go for an hour. The entire time, the CPU's temperature stayed at or under 60C (140F), a full 20C lower than the throttling point.'
Here <https://forums.theregister.co.uk/forum/all/2019/07/22/raspberry_pi_4_too_hot_to_handle/#c_3831920> is another suggestion: ... I got a heatsink for my 4G and just sticking an 8 inch tube of rolled card on the top of the heatsink to make a chimney knocks a good 15[°C] off it. This reminds me of the old “MacChimney” addon for the original fanless Apple Macintosh machines ...