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Drewstre
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50°c difference between CPU and coolant? [i7, Corsair 115]

Wed Aug 10, 2016 2:28 am

Hiya-
I'm trying to dial in some decent fan settings to make (and keep) a water-cooled overclocked i7-6700k happy. Relevant deets:

CPU: i7-6700k @ 4.5 GHz
Mobo: Gigabyte Gaming 7
Cooler: Corsair H115i
Case: Fractal Define R5
Goop: Arctic silver

The H115 radiator is in the roof of the R5, fans are blowing up (exhaust).

I'm running Prime 95 (blend) cranked up to 11 as we speak. I've set up a custom curve in Corsair Link, and after hours of tweaking, she's running a package temp of ~78°c stable. Groovy.

But the coolant shows a temperature of ~32°c solid.The coolant temp sensor in Corsair Link is simply labeled "H115i Temp". I'm assuming it's at the pump.

In Corsair Link, I'm setting the radiator fan speed to be relevant to the coolant temperature. It seems to be working well so far, but I haven't played Crysis yet. My question is, shouldn't the coolant temp be a bit closer to the temp of the thing it's cooling? After running pedal to metal for well over an hour?

My fear is that I don't have the pump seated properly, but I thought I'd check in before tearing back into this thing. Thanks to all for any suggestions.
 
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Re: 50°c difference between CPU and coolant? [i7, Corsair 11

Wed Aug 10, 2016 3:28 am

Try unplugging the radiator fans to see the temps move. If the CPU gets hotter at a higher rate than the coolant, I wouldn't trust the sensor very much.
 
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Re: 50°c difference between CPU and coolant? [i7, Corsair 11

Wed Aug 10, 2016 3:31 am

Yes the coolant temperature is about right assuming your PC lives somewhere where the ambient air temperature is <25 degrees Celsius (which is most places). Though I would have thought you'd be able to get much better than 78 C on the CPU.
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Re: 50°c difference between CPU and coolant? [i7, Corsair 11

Wed Aug 10, 2016 6:03 am

Seems like a pretty wide spread to me. Maybe you just got unlucky, and your CPU has a gap and/or poorly applied TIM inside the package between the die and the lid.

To rule out a coolant temperature sensor failure, feel the coolant return line from the radiator. At 32C it should not feel hot to the touch (just slightly warm).
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Re: 50°c difference between CPU and coolant? [i7, Corsair 11

Wed Aug 10, 2016 6:49 am

You can always try using your own Thermal Paste rather than what comes attached to the H115i. I actually went this route cleaning the TIM that came on and with my H115i and replaced it with Arctic Silver 5. I am getting about 64 C at the CPU and my H115i Temp shows the same as yours ~32C.
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Re: 50°c difference between CPU and coolant? [i7, Corsair 11

Wed Aug 10, 2016 7:56 am

You want a large delta between coolant and heat source.
The cooler your coolant the more efficient it is at taking heat from the processor.

If you measure the coolant temp going into the processor and again coming out you should see the cooling performance of your block and radiator.
In creasing the speed of the coolant flow will improve the performance of both.

Sounds like things are working just perfect to me if you are really worried try reapplying your tim.
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Re: 50°c difference between CPU and coolant? [i7, Corsair 11

Wed Aug 10, 2016 7:58 am

looks about right to me

what were you expecting?
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Re: 50°c difference between CPU and coolant? [i7, Corsair 11

Wed Aug 10, 2016 8:13 am

Aranarth wrote:
You want a large delta between coolant and heat source.
The cooler your coolant the more efficient it is at taking heat from the processor.

If you measure the coolant temp going into the processor and again coming out you should see the cooling performance of your block and radiator.
In creasing the speed of the coolant flow will improve the performance of both.

Sounds like things are working just perfect to me if you are really worried try reapplying your tim.

Yes and no. While a high thermal gradient will result in higher rate of heat transfer, it is also a symptom of an awful lot of thermal resistance between the die and the waterblock. Unfortunately, the most likely culprit is the interface between the die and the lid, which can only be fixed by de-lidding.
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Re: 50°c difference between CPU and coolant? [i7, Corsair 11

Wed Aug 10, 2016 8:23 am

just brew it! wrote:
Unfortunately, the most likely culprit is the interface between the die and the lid, which can only be fixed by de-lidding.


100% true. I just returned a 6700K to Microcenter because after multiple heatsink testing it just ran WAY too hot for comfort even at stock, and that was in a open case.
 
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Re: 50°c difference between CPU and coolant? [i7, Corsair 11

Wed Aug 10, 2016 8:38 am

just brew it! wrote:
Yes and no. While a high thermal gradient will result in higher rate of heat transfer, it is also a symptom of an awful lot of thermal resistance between the die and the waterblock. Unfortunately, the most likely culprit is the interface between the die and the lid, which can only be fixed by de-lidding.

This. Your flow is too low if you can measure a serious delta anywhere in the loop.

I measured this back when I had:

A highly clocked Phenom II X4
Two 4870X2 with full cover blocks

That's nearly a kilowatt of heat output, and the highest delta I could measure with my pump on low was around 1 C between the exit of the radiators and the exit of all the heat (CPU -> 4870X2 -> 4870X2 -> temp sensor -> radiator -> temp sensor).
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Re: 50°c difference between CPU and coolant? [i7, Corsair 11

Wed Aug 10, 2016 8:44 am

Dposcorp wrote:
just brew it! wrote:
Unfortunately, the most likely culprit is the interface between the die and the lid, which can only be fixed by de-lidding.

100% true. I just returned a 6700K to Microcenter because after multiple heatsink testing it just ran WAY too hot for comfort even at stock, and that was in a open case.

This is definitely a hidden downside to Intel's process superiority. Their ability to shrink their CPUs using the latest process means the thermal interface between the die and lid becomes the weak link for cooling, since the surface area available for heat transfer is so small.

Waco wrote:
This. Your flow is too low if you can measure a serious delta anywhere in the loop.

I measured this back when I had:

A highly clocked Phenom II X4
Two 4870X2 with full cover blocks

That's nearly a kilowatt of heat output, and the highest delta I could measure with my pump on low was around 1 C between the exit of the radiators and the exit of all the heat (CPU -> 4870X2 -> 4870X2 -> temp sensor -> radiator -> temp sensor).

I don't think the OP said anything about deltas in the cooling loop. AFAIK the 50C gradient is between his die temp and the coolant temp (not sure where the coolant temp was measured, I was assuming at the outlet of the radiator).
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Re: 50°c difference between CPU and coolant? [i7, Corsair 11

Wed Aug 10, 2016 12:41 pm

As I understand it, the coolant temperature sensor is likely to be measuring the incoming water temperature as it flows into the block.
If your room is at a 22C or something 32C is 10C over ambient which seems completely reasonable for what is probably about a 125W CPU load with that overclock. In most gaming PCs, the CPU is not the largest thermal load, not even when overclocked.

Is your GPU an exhausting blower type, or an open cooler that dumps its heat into the case? Either way (but especially if it's an open GPU cooler) you should be setting up your fan profiles with both prime and furmark running simultaneously. A 250W GPU with an open cooler will have far more effect on your Corsair 115's fan profiles than the CPU!
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Re: 50°c difference between CPU and coolant? [i7, Corsair 11

Wed Aug 10, 2016 1:45 pm

What voltage are you running your CPU at? With cooling of that grade, you could get away with pushing a lot of power through that chip.

I agree that the coolant temps are perfectly reasonable.
 
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Re: 50°c difference between CPU and coolant? [i7, Corsair 11

Thu Aug 11, 2016 1:16 am

just brew it! wrote:
Dposcorp wrote:
just brew it! wrote:
Unfortunately, the most likely culprit is the interface between the die and the lid, which can only be fixed by de-lidding.

100% true. I just returned a 6700K to Microcenter because after multiple heatsink testing it just ran WAY too hot for comfort even at stock, and that was in a open case.

This is definitely a hidden downside to Intel's process superiority. Their ability to shrink their CPUs using the latest process means the thermal interface between the die and lid becomes the weak link for cooling, since the surface area available for heat transfer is so small.

Waco wrote:
This. Your flow is too low if you can measure a serious delta anywhere in the loop.

I measured this back when I had:

A highly clocked Phenom II X4
Two 4870X2 with full cover blocks

That's nearly a kilowatt of heat output, and the highest delta I could measure with my pump on low was around 1 C between the exit of the radiators and the exit of all the heat (CPU -> 4870X2 -> 4870X2 -> temp sensor -> radiator -> temp sensor).

I don't think the OP said anything about deltas in the cooling loop. AFAIK the 50C gradient is between his die temp and the coolant temp (not sure where the coolant temp was measured, I was assuming at the outlet of the radiator).

Sorry, I wasn't clear. I thought you were talking about an in-loop gradient. I should learn to read more carefully! I should have replied to Aranarth.

My point is that it shouldn't matter where you measure in a loop at all, as the in loop temperature should be consistent within a very small window. If there is an in loop delta, something is wrong.
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Re: 50°c difference between CPU and coolant? [i7, Corsair 11

Thu Aug 11, 2016 2:04 am

Waco wrote:
My point is that it shouldn't matter where you measure in a loop at all, as the in loop temperature should be consistent within a very small window. If there is an in loop delta, something is wrong.

OT - I've never used an LC setup, so pardon the naïve question. If the difference in temperature is so low (e.g. entry and exit of radiator), then why do we have a radiator/fan setup, and why not just loop it around. If I had been asked to guess, I'd have just assumed (without any empirical evidence) that the radiator would have cooled the coolant by 10 degrees if not more. Maybe I'm just confusing the behaviour of automotive radiators/intercoolers with this. :)
 
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Re: 50°c difference between CPU and coolant? [i7, Corsair 11

Thu Aug 11, 2016 2:32 am

arunphilip wrote:
Waco wrote:
My point is that it shouldn't matter where you measure in a loop at all, as the in loop temperature should be consistent within a very small window. If there is an in loop delta, something is wrong.

OT - I've never used an LC setup, so pardon the naïve question. If the difference in temperature is so low (e.g. entry and exit of radiator), then why do we have a radiator/fan setup, and why not just loop it around. If I had been asked to guess, I'd have just assumed (without any empirical evidence) that the radiator would have cooled the coolant by 10 degrees if not more. Maybe I'm just confusing the behaviour of automotive radiators/intercoolers with this. :)

The coolant should be moving through the loop fast enough to not measure a gradient. The radiator(s) is the only way to actually get heat out of the coolant (without it, temperatures would rise till things melted, water boiled, etc). The heat exchanger / radiator will technically be slightly more efficient with higher coolant temperatures, but the downside to that is highly increased temperatures at the devices you're cooling (CPU, GPU, etc) because of the poor flow rates.
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Re: 50°c difference between CPU and coolant? [i7, Corsair 11

Thu Aug 11, 2016 2:45 am

Unfortunately, I can tell you that things will start to melt before the water begins to boil. I still have the deformed lexan top to a Maze4 waterblock I bought years ago where I learned that first hand.
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Re: 50°c difference between CPU and coolant? [i7, Corsair 11

Thu Aug 11, 2016 3:50 am

Thanks to all for your help. I dunked a heap o cash into this build, I just want to make sure I get every penny's worth.

My reason for posting was because the coolant temp seemed low for such a high CPU temp. I had hoped that a high-end dedicated CPU cooling loop would wrestle an overclocked 6700k into don't-worry-about-it territory. But when my high-end cooler is balls out, circulating water too cold for tea, and my CPU is still notching up 78°c under load, I started to wonder if I could make it better.

Frugal- Hot-yoinking the rad fans certainly causes temps to go up. CPU is gonna get warmer than the coolant that's trying to cool it. Whatchu talkin' bout Willis?

Yogi- Ambient temp is about 70° Fahrenheit. Memphis area. Hotter than Hades outside, but the roomie, she likes it chilly in the house. 69°f it is. Out-friggin-rageous utility bills be damned. That's another angst-filled post. That aside, I was hoping for better than 78° too.

JBI- Well, I ran Prime95 for 20 minutes (cooling profile Performance... max everything), and felt both tubes from the CPU pump (not sure which is which). Both were equally cool to touch. No heat detected whatsoever. But I would like to say that fondling those tubes while my system was cranked to 11 gave me a bit of the heebie jeebies.

tanker27- I used Arctic Silver 5 from the get go. I might be dumb, but I ain't stup SQUIRREL

Aranarth- I get that cooler coolant is cool. But if the heat isn't getting transferred to the coolant, that ain't cool. I have no way of measuring the coolant on both sides of the block besides poking probes into the tubes. This is a closed loop, off-the-shelf cooler. It's like my Momma always said, "don't go poking probes into a sealed system". She was smart.

f0d- cooler temps from an expensive cooler? Cogent advice?

Dposcorp- what temps were you getting that caused you to return your 6700K?

Chrispy_- In the Corsair Link software, it's simply labeled "H115i Temp". So I dunno where it's reading the temp. I've looked around, but Google and Corsair's website are equally useless.

synthtel2- 220, 221, whatever it takes... Kidding, running at 1.35v I think.

----------
So, what's the verdict? Bad lid?

Thanks again to all
 
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Re: 50°c difference between CPU and coolant? [i7, Corsair 11

Thu Aug 11, 2016 6:37 am

Waco wrote:
just brew it! wrote:
I don't think the OP said anything about deltas in the cooling loop. AFAIK the 50C gradient is between his die temp and the coolant temp (not sure where the coolant temp was measured, I was assuming at the outlet of the radiator).

Sorry, I wasn't clear. I thought you were talking about an in-loop gradient. I should learn to read more carefully! I should have replied to Aranarth.

My point is that it shouldn't matter where you measure in a loop at all, as the in loop temperature should be consistent within a very small window. If there is an in loop delta, something is wrong.

Depending on your definition of "very small window", I suppose. Unless you're using some sort of phase change coolant, a gradient around the loop is NECESSARY in order for there to be any heat transfer. If there isn't a measurable gradient, then the cooling system isn't working!

Yes, faster flow rates will reduce the gradient. But that comes at a price (increased pump noise).
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Re: 50°c difference between CPU and coolant? [i7, Corsair 11

Thu Aug 11, 2016 8:04 am

Less than 1 C in the crazy loop I had, with a D5 Vario at minimum. I was measuring it to put to rest the concept that loop order matters, versus connecting things using the easiest/cleanest path. A D5 at minimum through 3 blocks and 2 radiators is still a reasonable amount of flow, but it's not much compared to most pumps at even half speed.

I wish I'd had a flow meter at the time.
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Re: 50°c difference between CPU and coolant? [i7, Corsair 11

Thu Aug 11, 2016 8:51 am

Drewstre wrote:
----------
So, what's the verdict? Bad lid?

Thanks again to all


First thing to do is just remount the cooler on the CPU. May be bad contact. And would be my no. 1 hunch on why you are getting 78C. I don't own a 6700K so don't have a great feel for the temps, but would've expected you to get under 60C at a minimum.

Second thing is just let the system settle for a day and then check again to see if it's still crap CPU temp.
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Re: 50°c difference between CPU and coolant? [i7, Corsair 11

Thu Aug 11, 2016 10:04 am

Drewstre wrote:
Aranarth- I get that cooler coolant is cool. But if the heat isn't getting transferred to the coolant, that ain't cool. I have no way of measuring the coolant on both sides of the block besides poking probes into the tubes. This is a closed loop, off-the-shelf cooler. It's like my Momma always said, "don't go poking probes into a sealed system". She was smart.

----------
So, what's the verdict? Bad lid?

Thanks again to all


I'd take a look at online reviews using that kit where they over clock using that particular chip and see what temps they show.

I beleive Hard OCP has one.
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Re: 50°c difference between CPU and coolant? [i7, Corsair 11

Thu Aug 11, 2016 2:30 pm

1.35V is basically stock - are you sure about that? If so, your chip has both some of the best silicon out there and one of the worst lids out there (a top candidate for de-lidding, if you've ever considered such a thing).
 
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Re: 50°c difference between CPU and coolant? [i7, Corsair 11

Thu Aug 11, 2016 2:47 pm

synthtel2 wrote:
1.35V is basically stock - are you sure about that?

Are *you* sure about that? A lot of sources around the 'net seem to think stock for that chip is 1.2V.
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Re: 50°c difference between CPU and coolant? [i7, Corsair 11

Thu Aug 11, 2016 3:06 pm

just brew it! wrote:
Are *you* sure about that? A lot of sources around the 'net seem to think stock for that chip is 1.2V.

Pretty sure, yeah. Reports I've been hearing for Skylake tend towards the 1.3x range, and a friend's 6700k did 1.36 out of the box. It does seem unreasonably high compared to previous chips (I too am still used to 1.3x representing a good OC, not stock). That's the reason for my concern over Skylake's durability - it's still got a datasheet max of 1.52V, but even stock they're only leaving about half the distance from that that they used to.

Edit: A link to my thread on this.
 
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Re: 50°c difference between CPU and coolant? [i7, Corsair 11

Thu Aug 11, 2016 11:04 pm

Right, so I double-checked in the BIOS, and it looks like my core voltage is set at 1.30v. I don't think I've monkeyed with it, so that's probably stock, at least for this mobo. But according to the Intel Extreme Tuning Utility, it varies pretty wildly. Just running that benchmark a coupla times, it fluctuates between 1.1930v and 1.3760v. Wacky.

I'm gonna remount the pump on the CPU (assuming I can find my darn Arctic Silver) being extra super mega careful. Will report back with results.

By the way, while looking for stress testers, I see some folks online saying that Linx (Linpack) is a better stressor for CPUs than Prime 95. Thoughts?

Thanks again to you all.
 
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Re: 50°c difference between CPU and coolant? [i7, Corsair 11

Fri Aug 12, 2016 12:06 am

Yup, sounds like great silicon and a bad lid. All's perfectly fine as it is.

Drewstre wrote:
By the way, while looking for stress testers, I see some folks online saying that Linx (Linpack) is a better stressor for CPUs than Prime 95. Thoughts?

Linpack makes ridiculous amounts of heat, but doesn't seem to be any better at finding actual problems than Prime95.

An OC could generally fail for two reasons: instability, or thermal throttling. Instability should send you back to the drawing board instantly, but it's really tough to damage modern CPUs via thermals, and synthetic benches (like Prime95 and Linpack) make a lot more heat than practical use does. You could have a heavy OC that runs 75C in normal use, 95C in Prime95, and insta-throttles with Linpack, and it'll be a perfectly practical and reliable system - but Linpack won't tell you so. (Hitting the thermal limit won't do damage so long as you don't stay there 24/7, it just makes the CPU downclock.) Because of this, high-heat tests tend to underestimate how much of an OC you can run, sometimes by quite a lot.

Personally, I use Prime95 with large FFT sizes, so it tests the uncore more and has relatively low heat production (closer to the high end of practical loads). I find settings that pass that for 24 hours, then back off the clock by 100 or 200 MHz to give an error margin (I like wide error margins for that and am picky about keeping voltages low - most people would just bump the voltage another ~30 mV). For thermals, as long as my normal use doesn't take it past ~80C for sustained periods, I don't much care what Prime95 says.
 
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Re: 50°c difference between CPU and coolant? [i7, Corsair 11

Fri Aug 12, 2016 8:35 am

Drewstre wrote:
Dposcorp- what temps were you getting that caused you to return your 6700K?


Some cores would hit 90 degrees Celsius, and cause the CPU to throttle a few minutes into prime 95 (max heat setting)

I tried multiple aftermarkets heatsinks, and 2 types of thermal paste.......no change.
Every other CPU i tried with the same heatsinks has no issue at all, including a i3-6100 and a i7-950.

Also, to avoid any testing variations, I clear the CMOS and then set the bios to "default" setting when I first install a chip.

That particular 6700K was probably the hottest chip I ran in the last 6-7 years
 
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Re: 50°c difference between CPU and coolant? [i7, Corsair 115]

Mon Oct 10, 2016 4:15 am

Did you have a chance to re-mount and re-test¿

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