Rx 480 reference fan won't spin faster and card won't throttle itself under load

Jan 27, 2019
Recently I bought a second hand Sapphire reference rx 480 8gb and I'm quite happy with my purchase in spite of the following weird problem: with fan control set to Automatic in Wattman when the GPU is under full load its fan won't spin faster than ~40% even while the it is frying at 90 degrees Celsius. I expected some thermal throttling too but nada: the beast runs at over 90 degrees at the boosted clock and won't increase fan speed to save itself. When I set up a custom fan curve I can maintain the target temperature of 80 even though it sounds like a jet engine but the automatic mode seems to not be working correctly.

At this point I think that perhaps there is something wrong with the sensor: at first I gamed for a few hours on automatic mode blissfully unaware of the issue. Surely at 90 degrees the GPU should have shut itself down after some time but encountered no such issue. Could it be that the Wattman's automatic fan curve knows better and the 90 degrees results I get are incorrect?

Important note: since I got the GPU from a miner, a friend advised me to flash the bios in case it was modified for mining. I did that and used the following bios: https://www.techpowerup.com/vgabios/185131/sapphire-rx480-8192-160603-1
which is supposed to be the GPU's original. When I ran the program which flashed the bios, it indeed showed me that the bios I was about to install was different than the GPU's current bios. At the time I thought that the GPU just had a ming bios or something and thought nothing of it but now that I think of it perhaps the old bios was actually original and this new bios I installed is causing me these thermal issues? What should I do?

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