Is it normal for a CPU to get this hot under these conditions ?

Pekoms · October 21, 2018

Asking for a friend.

System:
Motherboars Asus Strix B350F
CPU Ryzen 5 1600
RAM Patriot Viper 4 16gb 3200mhz
SSD Adata SX8200 240gb
HDD Seagate 2TB ST2000DM008
GPU Asus Strix 1070 Ti Advanced Edition
PSU Corsair RM750X (2018)

CPU seems stable at 4ghz - 1.35625 volts, did a Prime95 Blend test (cause Small FFT's run way too hot), and it ran at 85 degrees in an hour, but I kind of expected that on Stock Cooler.
However, at 3.6ghz - 1.3 volts it runs at 84 degrees in Prime95 Small FFT's, 3.7 ghz going all the way to 89 degrees. (Stock cooler, Premium Thermal Paste - Cooler Master MasterGel Maker Nano, and yes, it was applied correctly, pea size, which I had to check because I had to disassemble the PC)

Is this normal, or could it be influenced by a faulty motherboard ? Why faulty ? Well, the build was really unstable, and 3 components were sent to Warranty, the Motherboard, CPU and RAM. Motherboard was checked as being fine, while the CPU and RAM were replaced. However, when the new components came, the system felt even more unstable, me being certain of two things. The new kit of RAM being another faulty one, and the motherboard wasn't tested the right way (both sticks of RAM give 0 errors on ONLY the B1 slot of the Motherboard, but the stick of RAM that seems to make errors faster that the other has a chance to prevent the system from booting, regardless of slot, the LED near the RAM getting stuck on Orange)

My friend already plans on buying a good cooler, since 4ghz is worth it, I just wanted to make sure if this is normal behavior or if it's influenced by the motherboard. A cheap™ but good cooler seems to be the Scyther Mugen 5 Rev. B. Do you think it can handle 4ghz while keeping the CPU under 75 degrees celsius ?