I have an i5 8400 with a stock cooler, Arctic Silver paste. At idle I get 24-30 degrees(by idle i mean chrome and discord open with steam running in the background), but after turning on a miner and leaving it at 100%, after 2 mins the CPU stayed steady at 52-58 degrees. That's almost double my idle and I'm pretty sure that's not good but then again I am not a cooling fanatic.