I've seen that a lot of people are having issues with overheating with Zen 2, and I've tried a lot of the suggestions, but I wanted to add what's unique about my particular problems to see if maybe there's something I'm doing wrong.
I have an ASRock B450M Steel Legend motherboard with the latest bios on that board (2.5). I've had to disable PBO to get it to stop overclocking to 4.2Ghz on all cores, so that's something abnormal, at least. My idle temps were high when it was OC on all cores, but since changing that setting have been 35-45C.
My case opens easily so I can test "open bench" and I'm still getting mostly the same results open or closed, so I don't think case cooling is the issue. I'm using an IC Graphite Cooling Pad instead of thermal paste, and from what I've seen in reviews, that might or might not increase my temps by 1-3C, but it shouldn't be more than that. I'm using the stock, Wraith Stealth cooler, and I checked to make sure all screws are even, there's no "play" between cooler and board, and screws are tightened down till the springs make a popping noise (which I think indicates they can't be tightened any more?).
When I run Cinebench R20 once, the CPU reaches 93C. When I run it immediately again, it reaches 95C. This is troubling because I intend to at least occasionally use this computer to render CG films created in Maya (and likely rendered in Arnold), though I'm sure the Cinebench test still uses more CPU-intensive rendering tasks than I will probably ever throw at this machine with my films. I only mention the intended use because I know most people who use these CPUs use them for gaming, and that is not my intended purpose for this build. So, while I'm sure the CPU will run cooler in games, if it runs THIS HOT during a marathon rendering session, that could still cause damage (could it not?)
What's interesting is that this machine, even while running on an old bios that made the CPU cooler run slower than it should've (and I'm not 100% sure it's running as fast as it should be now-- is 2000 RPM really the max. speed of this cooler?) has been completely stable... in its short life (1 week) it has never crashed or even slowed down while doing other things during a Prime95 test that was keeping my CPU at 95C. The CPU also never seems to really throttle at 95C. That makes me question whether something could be wrong with the temperature sensor, even.
I've seen a few people saying high temps are normal using benchmarking software, but 93-95 seems pretty crazy for Cinebench, and what Cinebench does is similar to what I'll be doing with the machine. I'm open to buying an aftermarket cooler, but it seems strange that I should need one to get safe temps when I'm not planning on overclocking.
Sorry for this super-long post, I'm just really frustrated that I'm not having any luck solving this problem.