[SOLVED] CPU temp seems to high even when idle

[drspyro]

Hi all

Over the past few months I noticed my desktop pc running really loudly even when idle. Upon closer examination (checking the case, also running CPU tests pushed the source of the sound way up) it seems to be the CPU.

CPU model is an Intel Core i5 8400 Hex Core LGA 1151-2 2.80 GHz CPU Processor

I ran core temp and while the pc is idle (mostly load <10) it runs generally around 55C, min 48C and max 100C on each of the 5 cores. I stress tested it using prime95 on the lowest test and all cores shot up to 100C within a second or two and stayed there during the test. After about a minute with all of them staying at 100 I just stopped the test out of concern something might go wrong.
The CPU is about a year and a half old. It seemed to run much quieter when I first installed it (it was part of a PC I built myself). I installed it without any modifications (standard fan, no fancy thermal paste). I am not sure how many months ago it started having issues.

Looking online it seemed like the temps I am getting are above what they should be (I heard around 40+ idling or 80+ under load was a problem. I don't know much about the topic so wanted to know whether these results were a sign of a problem.
If it is a problem, should I be trying to fix it myself or contacting intel directly for a warranty repair/replacement?

EDIT SOLVED
I tried to follow intels warranty instructions and it required me to physically examine the chip for a serial number. The chip was covered in thermal paste so I had to remove it to find the number. Luckily I had some stored away and after getting the serial numbers re pasted it myself (I had put it off worried that it would void warranty).
Since I repasted the chip the temps are now 30s when idle. When I stress tested the temp rose to 60 initially and 70s after a few minutes.

 

[Diddly]

Have you take the side of the case and checked for dust in the cpu cooler? If the case & cooler are full of dust that will cause overheating, you need to remove all the dust.

 

[drspyro]

Thanks. There was no dust but I did find a solution.
I tried to follow intels warranty instructions and it required me to physically examine the chip for a serial number. The chip was covered in thermal paste so I had to remove it to find the number. Luckily I had some stored away and after getting the serial numbers re pasted it myself (I had put it off worried that it would void warranty).
Since I repasted the chip the temps are now 30s when idle. When I stress tested the temp rose to 60 initially and 70s after a few minutes.

 

[mdd1963]

During i5-8400 CPU testing by Hardware Unboxed (you can find their channel on Youtube)a couple years ago, they pretty much reported the factory cooler as being sub-marginal for handling any sort of load without throttling....

Unfortunately, you can't expect much of a prompt rescue from Intel if your symptoms are mostly 'i don't like hearing my fan's whine under load'... not even 'my CPU hits 100C under a turture test' will do for getting assistance. You can try a larger fan that is less obtrusive blowing air across the heatsink if it is mostly the noise bothering you...or, get a bigger sink/fan assembly, as most accept as being necessary...

Replace it with a Scythe Mugen5 or similar...

(EDIT: Re-pasting some thermal compound helped that much? Awesome, great news!)