CPU really hot, but restarting PC will make it normal again

[Spitfire_2]

I can play AAA Games for 12 hours just fine below at 65 celcius,

But, when i went to sleep and let my PC idle,
the next morning/afternoon the CPU was idling at 60 celcius, when i ran Unigine Heaven Benchmark or any Games, it could reach to 100 celcius.

However when i restarted it(without physical fix), everything back to normal again.

What causes it? it was not like this before, this happened since i cleaned my PC (Removing Heatsink H60 included).

It has happened in the last 3 days

i5 6600 and Corsair H60 Liquid Cooling

 

[lfkfkfkffs]

your cooler isn't mounted correctly most likely.

 

[Spitfire_2]

your cooler isn't mounted correctly most likely.

i did more than 3 times, at first i thought it was fixed, but still happening if i let my pc idle when i asleep.

But i realize, a simple restart actually fixed it (for a while), but it always happen everyday

Pump and Fan all working, CPU usage all low.

 

[Richez]

Maybe your pump isnt actually working and after a while of it being on the pump actually starts to fail

If u feel like this could be a cause replace the h60 with a cooler master hyper 212 or decent air cooler of your choice

 

[sr1030nx]

I agree with the above poster, it may be your cooler, try a different one and check the results.