Yeah, I will try remounting the existing AIO once more, and next week I will be able to try out the setup with a Corsair iCUE H115i instead.
I am HOPING that it would be a cooler issue. Just don't know at which point I can rule it out as a potential cause for problems...
If you could sent at screenshot of the P-core VID voltages it might give another clue.
From what i know is that if your ambient temperature is 25° to 30° or hotter in this summer, those temperatures are normal for a 280 Aio if only some of the cores are peaking that temperature.
If all P-cores are constantly at 80-90° i agree that there might be an issue with mounting or microcode of Bios.
1.45v Vid is extremly unnessesary to achive advertised 5.4 Ghz. 1.35v is defenetly enough and most of the 13700k's can do 1.3v or even lower. I had the same issue as you with the ROG B-760-F and changed to a Z-690 because B-Series Motherboards doesn't let you proper undervoltage it . Really annoying!.
With an 360 Aio you will achive greater results but don't expect too much of a temp drop at that voltages trust me.
One thing that might fix your temperature issue is the Microcode of the Bios.
You can find that tweak under "tweakers paradise" or just use search if you dont have tweakers paradise. Then choose "old microcode" and restard. With that way, my CPU temperature dropped by 10-15°C at the same voltage on B-760. Really weird but they updated it in a later bios but i cant see that fix in your motherboard at ASUS support side. I would give it a try!
It made me smile to read your message because I've been writing on the internet (as well as emailing ASUS, which is incapable of effectively addressing my technical support request) for 10 months now, pointing out that the B660 and B760 motherboards with 13th-generation Intel processors have overvoltage issues. Changing your cooling system won't make a difference; the only solution is to revert to the BIOS I mentioned. The truth is that ASUS's software part (BIOS) is becoming increasingly chaotic, and their customer service is just as bad! I have an ASUS monitor that isn't working properly; they asked for the invoice, and now I've been waiting for their response for 10 days. ASUS is expensive, and yet their customer service is terrible. I know it's not easy to trust another brand; they all have their flaws, but switch to a different brand, and you'll see, you won't have more problems, and you'll pay less. I'm repeating myself, but this temperature issue is very noticeable and apparently only affects ASUS—it's incredible that they haven't noticed and fixed it.
******ty to hear about the situation. I am still waiting for my new AIO cooler and hearing this does not make me feel good either, obviously 🙂
I have yet to try the BIOS version you mentioned, was it version 2012 you meant? I wonder if there are any downsides that you've noticed by downgrading?
On another note, I repasted my current AIO once more, but it had no effect on the temps.