MacBook Pro suddenly restarts. Causes?

Question

Iron

Friends, there is a macbook pro 13 early 2011. What happened to him before he came to me is not known, but he arrived with a dead hard drive.
Disk removed and replaced with ssd. Accordingly, I installed OSX 10.10 on it and everything seems to be fine. But the machine itself, at a random time, just periodically reboots in operation.
Hmm, I thought that he didn’t like the ssd, pulled out the Apple hdd from the old mac mini, stuck it in it, the situation has not changed.
Is it worth looking in the direction of memory ?! Or maybe there is where to look because of what he is behaving like that ?! Or maybe it's just stupidly his time has come ?!
By the way, I found such an interesting piece of information that macbooks about 11 years old can be repaired by epl people themselves for free under warranty www.ferra.ru/ru/notebooks/news/2015/02/20/apple-ma...
Your opinion, friends, what to do?

Answer 1

Watch the logs - look for a soft reason for rebooting there. Maybe it's just a crookedly configured automatic reboot to install updates, or maybe some critical software error.
If there are no confirmations for software errors, then dig towards the hardware.

Answer 2

overheat

Answer 3

I suspect that he does not like memory, namely timings. Mac Memory has 9-9-9-24 and the one that has 8-8-8-22 in it.
This MacBook is a complete mystery, what happened to it is not known, but outwardly it is not kotsany ...