all provided everything is on auto in sys bios (no oc), hence the mobo can adjust at will, it sounds like there is a card/cooler problem. If your dealer is local I would have the card tested (or returned). With an open case your temps should be about 10C better than you see.
You have checked for a bios update via AGE?
otherwise I am out of ideas.. except you want to reapply some thermal goo but I wouldn't with a new card.
I am convinced it is that I lost on the silicon lottery this time. All of the reviews get cherry picked cards and I'm sure I just got an average or worse chip. I have been Googling info on Vega64 and this is a common issue I am finding. Most undervolt and usually overclock with success or most underclock a few MHz.
I'm just not going to the trouble. If it can't work out of the box, then I'm going to pass. Sadly I will go with GTX 1080 (I have freesync monitors) so I'm going to lose out. But AMD are just pushing these cards too hard and if you don't get optimal chips, you get issues.
I am in the same boat with my RX 480. I sold my old reference card to a friend that needed one and bought one with a good cooler with triple fans. It has been nothing but a headache. I RMA'd it three months ago and have returned two of the cards they sent me as one didn't work at all, the other crashed when I load any 3D games. They claimed to have tested them, but they obviously didn't. Boxes arrived undamaged and my computer room is static free and I use anti-static wrist pads and floor mats.
Now I bought this Vega64 as I needed a card and it came down to original pricing finally and bought it, but now I have the same exact issues as the RX 480. Except the 480's never overheated. But I didn't check until it started crashing with sound still playing. By then it must have degraded or just damaged something so it didn't get hot anymore.
What is AGE? My card didn't come with a DVD. I assume you mean a firmware update for the card? My motherboard is up to date on the BIOS.
I was thinking it may be the paste, but I'm not going to mess with a brand new card. I did that once and voided the warranty and it wasn't honored. And it was a GTX 9800x2. Luckily it worked fine, just had a horrible whine as some resister or something casing broke in half. I superglued the housing back on and it luckily worked.
And no, I don't overclock. I've learned over the years that it is just not worth it. I've learned every program stresses the computer differently and one program can be stable while another will be unstable. Plus there is usually such a small increase in FPS that it just isn't worth the hassles.
Thanks for the help.