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System throttles under heavy load with default BIOS settings - cooling problem?

Level 9
Greetings all,

When I got my i7-8700K, I delided it right away, w/o doing any tests. But now have some concerns.

Here is my system:
Asus prime z370-a
AiO 240mm water cooler (alphacool eisbaer LT240)
64GB GSkill @3200 xpm profile
default BIOS settings (max-turbo 4.3 on all cores)

My idle temps are 29-32 degrees and idle power draw (wall socket) is 32.5 Watts, and when I run the heaviest benchmark I know of (Intel Linpack) I see that it starts to run at 4.3 Ghz on all cores (default settings for CPU bar 3200 XMP profile for 64GB RAM), temperatures reach 70 degrees, power draw reaches 220 W and in few minutes I can see the system throttles to as low as 4.0 GHz synchronous on all cores.

Benchmark results then varies from 364.7 max (no throttling) to 356.3 average on 10 runs, of which I think at least 8 are at least partially throttled.

I am tending to think that under default settings CPU should not throttle from default 4.3 tubro-freq even under the heaviest workloads. Am I right? Or only the base 3.7 freq is guaranteed and I should consider self lucky that it even runs above the base on the deffault settings?

If it's the former, does this mean I messed up my thermal interface when deliding? I.e. too little liquid metal, or too thick lid gasket, or something else?

Prime95 in torture mode does the same.
It starts at turbo-max 4.3 w/o throttling, stays at 60 degrees, and draws 190 W of wall socket power. But then I see it switches to smaller FFT sizes and throttling kicks the freq down to 3.7 (it then oscillates between base and max-turbo) . Max power draw I was 209, and some 67 temperature.
Too bad prime95 in torture mode posts variable load!

So if you find this is all fine, what's my OC potential then?

Thanks in advance!

Level 10
Hello metadist,

welcome. Best to rule things out, bit by bit.
I personally would (sadly) beginn to accept that 64GB RAM is awesome but taxing the CPU as well due to the controller beeing backed in.
Start with 1-max 2 sticks from now on.

"XMP" modifies more than one value in the Bios
VCCIO voltage
system agent voltage
beside the ususal
DRAM voltage
are beeing modified to cope.
Many times you can get stable using rather less voltage than the preconfigured "XMP" setting will set.

Kindly download HWinfo64 and get comfortable with it.
There are tabs for many throtteling issues.
This may help to dial down which part gets overtaxed first. Kindly run the stresstest of your choice and share your results if you like.
Intels overclocking tool ( XTU) has a good graph and other monitors that can show many different theraml issues.


If possible use half the RAM for tesing puroses ( you will have to bump the voltage afterwards. At least know you know what 64GB draw compared to 32/16.)

check XMPs VCCIO and system agent idle voltage in bios and kindly share

The are at least 2 articles with links to a graph that shows standard voltages for different size of kits.
Try manually setting your Ram
DRAM voltage according to specs
VCCIO according to the article researched
System Agent according to the article researched
All according to the RAM Size you end up testing

Good Luck and Best Regards

Hi Carlyle,

Thanks for the valuable advise!
I have experimented with less RAM and saw the following:
32GB (2 sticks) - the same as 64GB, i.e. CPU throttling after some 10-15 minutes of heavy load.
16GB (1 stick) - NO throttling.

In the bios I see the following values: VCCIO 0.952, SA 1.064. But I am not sure they are not adapted, since I am on a default (yet) settings, with everything Auto.

This is a bit encouraging, since, like you said, I can still try manual settings of VCCIO and System Agent in hope to keep power usage down.

From the other side this adds another dimension to my project, which I hoped to avoid...

Another piece of rant someone may enjoy:

My first OCed system was Pentium 120. CPU frequency multiplier had to be set manually with a combination of jumpers on the mainboard. I have set it to overclock to 150 - worked. No multiplier lock was invented back then.

My second OCed CPU was Celeron 300A in a Slot1 formfactor. This was first introduction of Celeron line, they differentiated it by lower FSB - 100 vs. 133 for Pentium II and III. However the Celerons had larger cache. One setting in BIOS could change FSB to 133 and 300A used to become Pentium II 450 instantly. The board was an iconic Abit-BH6 which served me almost 10 years, which was explained by unique upgradability potential of the Intel platform back then. It supported Celeron 1400 as it's max with just a bios update. Which was almost 5 times the CPU it originally supported!

Nowdays I'd say Overclocking is a mixture of art and science, and hats off to the profies who excell at it so much!

Thanks again!

Level 10
Trial and Error Method for me most of times 🙂

Your PC History was fun to read and did bring back some memories. Good and bad 🙂

Your idle voltages are rather very low o be honest.
Did you make the pics with only 16 Gig installed?

I would think, that 64 Gig would need 1.2 -1.35 on both....
Try 1.2 to start with fully kitted with 64 Gb .
Put a little difference in power between both .
Some write that the HW likes it.

I rather think your throtteling may even have something todo with not enough power.
I would even be more convinced of this if your idle power states mentioned would have been made with 64 Gig intsalled.


The Asus Guru himself has sage advice and the graph i mentioned in the first post:

Thanks again, Carlyle!
Yes, the values were for default optoins.

I have since increased them, and now the read, for the full 64Gb: VCCIO=1.15 , SA=1.19

I have set Adaptive mode with vcore limited to 1.36, and LLC=4.
I figured this allows to adjust VCCIO and SA for heavy load, while keeping Vcore capped. At 1.36 it's already enough for 5.0GHz max turbo and AVX offset=2
I'll now fight a bit for bringing the AVX offset to 0, since my apps are math heavy and would benefit from faster execution. But it might be already impossible.
I left uncore settings to Auto.

I have also updated my other post about Linux with some more details on using benchmark and monitoring tools under Linux.