Question about thermal paste and more!

Oct 6, 2018
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Hello,
I have recently upgraded from a Cooler Master MasterLiquid Lite 120 to a Corsair H110i GTX 280 for my i7 8700K, so here's the thing, the first time i applied the thermal paste i did the regular dot method and that kinda made it so that my CPU was still running hot, the next time around i tried the spread method which actually made temps a lot better but this is where my issue is, the temps were decent but like.. 2 days later the temps started going up again all the way to 100c, now I kinda re-did the whole thing again and now temps are around 75-78c ish under somewhat heavy 100% load and i say that because some tests seem to have different stress even at a 100% usage, and i primarily wanna know if there's anything i could have done wrong to make it so that the CPU would start heating up 2 days later without actually touching my internals at all.. the only things worth mentioning that i did was increasing the voltage a bit but that was before testing in which case i realized the temps were pretty good still, so is there anything i could have done to cause this to happen or hopefully prevent me having to disassemble my PC again just to re-apply thermal paste ?
 
I believe that there has not been variation in two days. I think it is due to the fact that liquid cooling has lower temperatures in the first minutes and after about 30 minutes, when the liquid has warmed up, the temperature rises somewhat and stabilizes.