Max temperature on linksys WRT1900ACS V2


I bought this router WRT1900ACS V2 recently and installed latest version of openwrt on it. After finished all my configuration I lost connection.
So I started the investigation. Observed same behavior on linksys firmware. Around 10 or 20 minutes after put router up, it reboot and no more connection. I have to put off wait a bit and put up.
I passed all my search and my conclusion was "the temperature"
I added a fan on the top and since this time, router is up and running.
If I remove the fan and when temperature is going more then 61°C, router reboot.

I have another linksys WRT1900AC V2 (not exactly same model) and when I check temperature, it is much more (around 70°C 75°C) and no reboot.
I suspected it was due to the thermal pad. I replaced it by a new one but still the same. Without any fan, router reboot.

Is it a know problem on WRT1900ACS V2 ?
Could be link to a hardware problem on router ?
The threshold is defined in kernel or it is hardware protection ?
Is it possible to have more info by checking log from serial cable directly on the board ?

Thanks in advance.


Neither. It crashes, it's not protection of any kind.