Some versions of prime cause overheating.
Try using a different benchmark such as super pi or cinebench. If you get similar temperatures, you are definitely running too hot,
Watercooling should be plenty. Check thermal paste, pump, fans etc.
Once you have your cooling sorted, check your Vcore: 1.33V is too much - will reduce the life of your CPU. Set Vcore in bios to 1.25V (don't leave it set to Auto). See how fast your CPU will run now. Should be at least 4.4Ghz