I have a Pi3 in a fairly enclosed environment, and I found that, even when my Pi was relatively idle (5% CPU usage) the CPU temp was averaging around 80C, which is close to the 85C where the Pi starts to underclock and the 90C where the Pi starts to get damaged. Since I'm planning some more processor-hungry tasks, I want beef up the cooling, if only for performance reasons.
I already have a heatsink on the Pi's main chip, so I'm considering adding a very small fan. I found that even slightly blowing on the chip immediately takes the temp down to 60, so it's entirely an air-flow problem, so even a very weak tiny fan should work.
Unfortunately, I don't have any more room to add a power regulator to supply the fan, so I need to power it directly from the Pi's 5V power rail and controlled via a GPIO pin. What are the fan specs I should be looking for so it doesn't exceed the Pi's max current? Is anyone aware of any very tiny and silent 3.3V or 5V fans suitable for this?