My new Intel 8th Gen Core i7-8700K Processor

[EarthDog]

If you are auto overclocking, it is likely a -3 AVX offset causing the CPU speed to drop. VRM throttling drops it much lower.

 

[marjamar]

Been doing a bit of overclocking this CPU. I can keep the core speed stable at 5 GHz, and I can keep the vcore set in BIOS to 1.4v and run prime torture Blend without problems holding temps from 55 to 78 or so, mostly around 65. Can't run Small FFT's though, temps just jump to 100 in an instant while holding 5GHz. It would keep running, but I stop the run as that is too high to play with. This is happening because I have CPU Load-Line at 7 to handle the fluctuating current demands running Prime95. Tried it at 6, but I would have to raise the vcore above 1.4, which is about as high as I would like to have it. I have never had a CPU run temps up so quick before. Makes me wonder if I'm having a problem with the CPU waterblock getting proper thermal transfer from the CPU, or maybe the CPU itself is not transferring heat to the CPU lid. Either way, I will be limited in driving this CPU hard with a overclock anyplace close to 5 GHz unless I figure this out. So, obviously this is why the CPU was throttling back to 4.7GHz, too much internal heat in the CPU not be absorbed well enough though the cooling system. I think I can understand better the idea of delidding, HA!

-Rodger

 

[EarthDog]

That isn't happening because of LLC. That is happening because Small FFT is more stressful and runs CPUs a lot hotter than blend.

Since you are hitting 100C, chances are you are seeing thermal throttling. When running blend, do the clocks drop to 4.7 GHz as well?

What is your actual load voltage? Not what is set in the BIOS, but what does CPUz or Hwinfo or w/e say your load voltage is set at?

If Hwinfo will tell you throttling reasons, or have Intel XTU running with P95 and look to see what it says (at the bottom, may need to expand that space at the bottom to see it all).

 

[marjamar]

That isn't happening because of LLC. That is happening because Small FFT is more stressful and runs CPUs a lot hotter than blend.

Since you are hitting 100C, chances are you are seeing thermal throttling. When running blend, do the clocks drop to 4.7 GHz as well?

What is your actual load voltage? Not what is set in the BIOS, but what does CPUz or Hwinfo or w/e say your load voltage is set at?

If Hwinfo will tell you throttling reasons, or have Intel XTU running with P95 and look to see what it says (at the bottom, may need to expand that space at the bottom to see it all).

At idle, vcore is from 1.39-1.404. Under Max load, it's 1.44 at 5GHz.

-Rodger

 

[EarthDog]

Not sure why your preference is to have it raise under load... but Ok.

If you would like to get down to the bottom of your endeavors.....

When running blend, do the clocks drop to 4.7 GHz as well?

If Hwinfo will tell you throttling reasons, or have Intel XTU running with P95 and look to see what it says (at the bottom, may need to expand that space at the bottom to see it all).

 

[marjamar]

I've set AVX instruction offset set to zero, and I have sync'd all cores to 5.0GHz, so I am seeing 5GHz always - Load or no load. As to the voltage going up under max load, that's what with CPU load-line is for. If the demands for more current occur, the higher the the settings level you use, the more the vcore will rise to provide the necessary current level without voltage drop/droop. Ideally, I would suppose having a constant absolute voltage would be the better way to do this, but to keep the CPU stable under max load, it seems it is always a case where the vcore must raise when current demand raises and using the max setting I am, it will rise faster and higher then the load will.

I think I will do some research on delidding. I use Arctic Silver 5 TIM and have for many years believed it to be top level TIM, so unless I am missing something, the super fast rise I am seeing in CPU temps at max load must be a less then suitable internal thermal transfer condition, which I have heard is not uncommon. I guess I could send the CPU back for exchange, but I have only done that once years ago and I do not like returning something that is about normal or par for the course. Never have delidded before, so I am not at all familiar with the process used. I understand there are kits for this, so I will take a look and find out more before deciding.

-Rodger

 

[EarthDog]

Ok, so its temperature throttling then. Since you likely do not run AVX, you can probably use an offset and lower vcore to boot.

AS5 is frighteningly mediocre TIM. Its 1-2C behind anything non metal.

 

[wingman99]

For 5.0GHz you should not need more than 1.40V Vcore under load. Folks that run prime95 and 5.0GHz delid.

 

[marjamar]

I have a ordered this - Thermal Grizzly Kryonaut Thermal Grease Paste - 1.0 Gram. I want to make sure my CPU water block is pulling as much heat as it can from the CPU lid. I am only seeing about .5 C difference between inlet and outlet temps at the 360 rad which is about all I have ever seen with this loop. I wonder what people are seeing with a delidded i7-8700K under full load at 5GHz clock on a single 360 rad with a push/pull setup.

-Rodger

 

[EarthDog]

That's about right. A properly sized and flowing loop only shows around 1C or so difference at any point in the loop.

 

[habbajabba]

Tinker Tailor Soldier Spy, I mean Roger. Nice setup. That setup is like overkill or what? At 5ghz you need some serious cooling on that 87.

 

[marjamar]

Well so far, after testing various overclock settings for a few hours, the best overclock is the factory extreme that came in this mb bios. Runs prime95 torture (any of them) the best with the coolest temps. Clocks down to 4.7GHz, but I cannot match how well it works, using my own 4.7GHz settings, for both CPU temps and low vcore. It really is the lowest vcore I've seen running under full load which is throttling of course to 4.7, but most of the time it's at 1.376 v or below. I'm going to wait for the new TIM to get here and see what happens with temps using this factory extreme setting before I get too excited to do too much more. I have see as much as .7 C difference from input to output temps at the rad ports using my aquacomputer flow through sensors (which are suppose to be very accurate), so am wondering if that will change at all, even if this new TIM transfers more heat from the CPU. I have a feeling I might actually need more rads in this loop to keep the water temp lower, as it does rise at least 2 or 3 C after a 20 minutes or so at full CPU load.

-Rodger

 

[EarthDog]

Temps will rise after 20 mins... a couple of reasons...

1. P95 has variable loads
2. It takes at least that amount of time to saturate the loop/reach an equilibrium. Its going to do that with 2x120 or more as well. When testing loops, normal heatup periods are, at minimum, 30 minutes for that reason(s).
3. 120mm rad isnt enough anyway for that heavy of an overclock. General rule of thumb is 100w for 120mm... you are likely pushing 150w with that overclock and voltage.


You would likely have the first motherboard ever to have automatically set the lowest possible voltage for the clockspeed.

You really wont see much chamge with paste. A couple C at most from paste alone. Any C helps in your case though!

As far as temp change from inlet to exhaust... not much as i said. 1c or so is about right. Its not like a car where, when the thermostat is closed it sits in the radiator... this is a constant flowing loop...the liquid doesnt stay in the rad for more than a couple/few seconds.

Edit: you have a 360 rad... please update your signature so we know what you have...

Obviously, you have plenty of rad...your loop was still in the process of saturating. Its nit a lack of rad area...

 

[marjamar]

Temps will rise after 20 mins... a couple of reasons...

1. P95 has variable loads
2. It takes at least that amount of time to saturate the loop/reach an equilibrium. Its going to do that with 2x120 or more as well. When testing cusr9m loops, nkrmal heatup periods are, at minimum, 30 minutes for that reason.

You would likely have the first motherboard ever to have automatically set the lowest possible voltage for the clockspeed.

Well that's only because I am so good at it!

-Rodger

 

[EarthDog]

Or, it isnt the lowest voltage.


Also, please note entire post above. Much was added.

 

[wingman99]

Well that's only because I am so good at it!

-Rodger

Post a screenshot of HWiNFO sensor readings under full processor utilization.

 

[marjamar]

Or, it isnt the lowest voltage.


Also, please note entire post above. Much was added.

Re-reading your updated previous post it seems I might need to delid if I do need lower CPU temps @ high clocks, as a couple of degrees isn't going to make a very big difference I do not believe. I've been watching videos and I can't say I am real impressed to do this. I know I can, but I also know I will most likely never be confronted with real heat issues unless I really need to have a strong overclock, which I don't really believe is necessary for anything I normally do. I will most likely use this computer as it finalizes without delidding, unless something comes up where I do really need to delid.

I'll change that rad in my signature block.

-Rodger

 

[EarthDog]

Yeah, really, you only need to settle on a clock that wont throttle and manually dial it in so you ar3 using the least amount of voltage possible and get the lowest temps.

 

[marjamar]

Post a screenshot of HWiNFO sensor readings under full processor utilization.

I can do that. Are you wanting to see the factory overclock or my overclock? Also, there are different thermal responses to different "full processor" utilizations. I can't even run Prime95 Torture small FFT's with my 5GHz overclock. It will hit a 100 C in just a few seconds and that's too high to play with for me. I can run that however using the factory 5GHz setting. My overclock holds 5 GHz, the factory throttles to 4.7GHz. Best I could do with my overclock is Prime95 Torture Blend setting which will be higher everything most likely then the factory overclock running small FFT's.

-Rodger

 

[EarthDog]

I can run that however using the factory 5GHz setting. My overclock holds 5 GHz, the factory throttles to 4.7GHz.

The 'factory' overclock should have the -3 avx offset IIRC. So i think there its an offset, not throttling considering your temps dont hit 100c.