I have bought a used rx580 4gb pulse, then when i tested the gpu in some games I noticed that the temperature where up to 85 °C, so i changed thermal paste. There wasn't much paste, but when I tested again the card nothing changed. It was probably in thermal throttling. It was doing less fps than my rx 460 2gb. Then also sometimes the fan went full speed and the screen went black, so I needed to restart my PC. The strange thing is than the temp were so high, but the card was not. I tried to underclock, give more power via radeon software, search if I had a mining bios, put the fans at full speed, but nothing changed.
In normal use it worked, when i started a game the card always went above its "security temp" of 84°C. So i got a refund and put back my old gpu. The seller said that i could keep the graphics card, so I'm trying to repair it, beacuse I don't like to thrown away things without trying. So if someone cuold help me I would be very grateful.
(Sorry if my English is not perfect, I'm not from US)