Question Best solution for high CPU temps ?

May 11, 2021
So, first of all, while I do have some knowledge of components, I am far from being an expert. Especially when it comes to hardware manipulation. The one who did the hardware manipulation on our PCs was my father, who died from covid-19 last year. As for me, well, I'm not exactly good with my hands so...

That being said, here's the situation. I have a desktop with an i7-5820k, cooled with a corsair water-cooler. In the past year, temps kept going higher and higher gradually.

Now, with 18 degrees ambient temperature, the CPU overall temperature reads ~70 degrees idle, and ~90 degrees at 40% load. Core temps themselves are a bit lower, at 65 and 85 respectively. Did I mention those temps are in Celsius ?...

So, here are the issues I thought of :

-1 : dust on fans
-2 : dried thermal paste
-3 : lack of liquid in the watercooling system
-4 : other watercooling issue.

I'll address them one by one :

-1 : There are two fans in that watercooling system, one easily accessible, and the other "in a sandwich" between a grid and a metal plate, which means hard to reach. While the first one had some dust on it, it was extremely thin, albeit it did dirty the cloth I used to remove the dust from it. The other one looks like it's in the same condition : thin, almost invisible dust on it, but I can't access it. While it's not very good, I think it's safe to assume that it's acceptable and not causing the issue here.

-2 : thermal paste was, from what I know, not replaced since temps were good (30-40 idle, 55-70 100% load) until one year ago. But since 2015, it should have dried up already by then, so I'm a bit doubtful. Especially since the pipe leading from the CPU to between the fans is quite hot, almost burning to the touch, even near the fans, so heat seems to be conducted from the cpu to the watercooling system...Should I replace it, and risk making a mistake?

-3 : I've read that water could evaporate from the watercooling system, making it less efficient. Should I risk opening it, probably loosening the seals in the process, and thus furthering (or creating) evaporation in the future? If yes, should I just check the liquid level somehow, and add some if necessary? Or should I fully replace it with distilled water&a bit of biocide? Where would I find those two by the way?

-4 : Is the watercooling system just not working properly anymore, especially the pump since it sometimes makes loud noises, and should I just replace it? By doing so, does that mean I would have to apply thermal paste? If that's the way to go, how do I make sure the new system is compatible with my motherboard/cpu/case? (I don't know exactly which watercooling system was installed in the first place, only its brand...)

My own guess is that the best way to solve the issue, which is also the one requiring more work&skill, is to just replace everything, watercooling system&thermal paste... If you simply agree with that, the only things I would like you to provide is how to get the right system, and point me towards a good, detailed, step-by-step, explanation video to do it...

Sorry for the length of this post, but I tried to address everything in one go instead of adding elements only if asked or even after using a proposed answer, only for it not to work well enough..

Thank you in advance for your (hopefully helpful enough for me to manage to address this issue) answers!


Apr 7, 2019
Should I replace it, and risk making a mistake?
There is no mistake in replacing thermal paste. Each time you lift the heatsink off from the CPU, you break the seal that was made in between the paste and the heatsink, essentially requiring you to replace the thermal paste anyway. Also replacing the thermal paste, you're basically refreshing your thermal paste so its a good thing.

If your CPU temps were higher over the years (i.e. increased idle temps) then I would suspect that the thermal paste may have possibly dried up, otherwise I don't personally find thermal paste to dry up exactly after the 5 year mark. I've been using thermal paste from even an Intel stock cooler that's used for 6-7 years and my CPU temps are still fine. It wouldn't hurt to check though your idle temps and possibly infer from it or replace your thermal paste in your case since your idle temps have increased over time.

For replacing thermal paste, you will need to wipe the old one off first before placing in a new one. You can use Isoprphyl Alcohol (70% will do, 99% is hard to come by). The most important thing though afterwards is to make sure that it is dry because the other 30% is made up of water. Alcohol dries fast and cleans the muck hence it is the recommended cleaning agent to be used. Only use the Isoprphyl Alcohol to clean the top of your CPU (I use cotton buds and soak them first in alcohol), don't soak your entire CPU on alcohol.

Don't use any abrasive material to clean your CPU from thermal paste. Tissue paper will do.

For starters, you should familiarize yourself with the dot method of applying thermal paste (Guide here , but you can check other youtube vids on how its done). It is the most simple and effective method and simply involves you placing a small pea sized dot of thermal paste to the CPU before you attach the cooler on top. Generally you want to avoid over spills as it will be a mess to clean up.

Since you're probably new to this, I would suggest using standard thermal paste and not liquid metal paste like Kryonaut from Thermal Grizzly. There are some fine nuances you need to know about those and you need to be extra careful with using liquid metal paste (i.e. don't use liquid metal paste on aluminum surfaces and be very careful not to spill it over, as it will be a mess to clean it up).

There are 2 types of water cooling solutions for PCs - AIOs and Custom loops. You most probably have what is known as an AIO (All in One) which generally does not require maintenance at all. Yes, water can evaporate from an AIO if the AIO is damaged in some way. Since you mentioned your pump is already making sounds + 5 years has passed, I would suggest getting a new AIO if you want to continue with water cooling. And yes, getting a new AIO - you must ensure that you put thermal paste onto your CPU, unless the AIO's heatsink already has a pre-applied thermal paste onto it.
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Number 4, yes.

That is a decent lifespan for an AIO. Probably on the way to pump failure, particularly if you are hearing noises from it. Either it is running dry, the pump bearing has gone bad, or the pump's blades have started to degrade. Caused by the fluid having evaporated, the biocide failing, or the mixed metals prevention getting used up. Copper and aluminum trading electrons and eating away at the cold plate.

i7-5820k is an LGA 2011 socket. Any cooler that supports that will work.

Would need more details on the chassis and the old cooler to pick something specific out. 120mm, 240mm, 280mm, 360mm radiator...,10240,10280,10360&sort=price&c=21,28