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Question

CPU fan speed not compensating for increases in heat.

by DaylonRuS / June 18, 2015 6:14 PM PDT

Before you read any further, you should know that I tried the obvious things like clearing the CPU fan and heatsink of dust, reapplying thermal paste, checking the fan for blockages, updating the bios, and cleaning then reseating the CPU fan pins. But if you want to mention another obvious thing that I may not have tried without reading the many paragraphs below, feel free to.


I have a 4 year old desktop build with an AMD Phenom processor and stock heatsink. It was running windows 7 most of this time and never had problems overheating or shutting down. I don’t know what my average temperature or fan speed was, but I can say with certainty that it never exceeded the 140F cutoff temperature that I set on the computer’s first boot. This includes the several times over the years that I have run benchmarks and stress tests which kept the processor at 100% usage for an extended period of time. Note: while I never recorded fan speeds or cpu temps, I know about how loud the fan was while the cpu was under heavy loads.

I recently installed Windows 8 on a different partition on the same hard drive and ran into a problem with the computer shutting off when under mild-medium loads. After a bit of snooping with software like Open Hardware Monitor, I found that the CPU was reaching its safety shutoff heat limit of 140F. Oddly, when I booted back into the Windows 7 on the other partition, I had no issues with the PC shutting down under any load. Regrettably, I never checked the CPU temps or fan speeds under different loads.

At a later time, my SSD came in the mail and I installed it then installed Windows 8 onto the SSD and erased the Windows files on the HDD. The CPU was still reaching temperatures high enough to shut down even when under light-middle loads. At this point I installed Open Hardware Monitor and started recording CPU temps and fan speeds. While idling in this configuration, the CPU temp tended to stay around 132F (which I believe is much higher than it typically was when running Windows 7, although I don’t have specific temperatures from then) and the fan speed stayed around 3300RPM. When even a small number of light programs were running, the temp would increase to 140F and the computer would shut down with no significant change in the CPU fan speed.

I rebooted the computer into the bios to check the CPU temp and fan speed. The results were the same, 132F and 3300RPM. I left the computer off overnight to see if booting straight into the bios would change the results. After letting the system cool completely and booting straight into the bios, the cpu temp started around room temp and heated up to 132F, while the fan speed stayed at 3300RPM the whole time, not increasing to compensate for the rise in temperature. I tried all of the different combinations of fan speed profiles, saving and resetting each time. None made any difference to the relationship between the fan speed and CPU temp, whether tested in the bios or in Windows 8.

At this point I bumped the CPU cutoff temp up to around 160F so I could measure higher temperatures without it shutting down. I tried completely restoring the bios settings back to defaults to see if it would fix the issue, but there was no change in the results. I also tried installing Speedfan, which I was told communicates with the bios to read temperatures and control fan speeds. As far as I could tell, it was not compatible with my system and was not affecting the CPU fan speed. To see what role windows played in the equation, I installed windows 7 onto a bootable flashdrive and booted it from the computer. While idling, fan speeds stayed steady around 4000RPM, which is the first change in fan speed since I had started measuring. CPU temp stayed below 110F, usually pretty close to 100F. However, when I opened up some medium load programs, the CPU temp increased to around 120F with no significant change in fan speed. I went ahead and ran a stress test to see if the computer was usable under these conditions, and the CPU quickly reached its heat threshold of 160F and shutdown. As usual, there was no significant change in fan speed during the stress test.

This is where it really starts to get pretty odd. After the tests on the Windows 7 drive, the computer was left off overnight. When booting the bios, the fan speeds were still at 4000RPM but the CPU temp rapidly rose back to its usual 132F. After letting it cool then booting back into Windows 8, the idle temp was still 132F with the fan speed consistently staying around 4000RPM.
Just to see if I could get some contrasted results, I installed the Windows 10 preview onto the HDD. After the installation but before first boot, I checked the bios stats. Temp stayed around 120F and fan speed around 3700RPM. I booted into windows 10 for the first time and let it idle after installing Open hardware monitor. I recorded fan speeds fluctuating a bit higher than on the bios (bobbing around 3750), and cpu temp a bit lower around 115F. I then started up a stress test to see if the fan speed would increase as the temp increased. It did gradually increase, but not enough to regulate the CPU temp. The fan was at 3750RPM when the CPU was at 135F, 3800RPM at 145F, and 3950RPM when I ended the test at around 155F.

When I next booted into the bios, after a complete cool, the CPU temp started around 90F and the fan around 3400RPM. Idling on the hardware monitor screen, the CPU gradually rose to 140F, with the fan following and eventually reaching 4000RPM. At that point, the fan stayed steady and the cpu dropped to 132F. While maintaining a temp of 132F, the fan very gradually rose to 4275RPM (the highest I had recorded to this point) and fluctuated. I then booted into Windows 8 on the SSD and got an idle reading of 130F 4200RPM. Under the stress test, the fan speed very slowly followed the temp from 130F 4200RPM to 170F 4450RPM, at which point the machine shut down. I doubled checked and the bios indeed indicated that the shutdown temperature was 160F, but for some reason it allowed the temperature to increase to 170F, which is inconsistent with its strict behavior when the safety point was 140F.

On a warm boot, the fan speed was recorded at 4700RPM, higher than it was when the stress test was actually taking place. The CPU temp held at 132F as the fan gradually dropped back to 4150, almost as if the temp was intentionally being maintained at 132F.
I installed windows 7 on the HDD, replacing the windows 10 preview. As with the flash drive, this installation of windows 7 had an idle of around 100F with a high fan speed, around 3700RPM. Under the stress test, the Fan speed rose gradually to only about 4000RPM as the temp reached 170F and the machine shut off.

My specs are:

AMD Phenom ii 975
BIOSTAR 870U3 AM3 870
PNY 2x2GB XLR8
GIGABYTE GV-R927XOC-4GD Radeon R9 270X 4GB
Mushkin MKNSSDEC240GB 2.5" 240GB SSD
2TB Hitachi 3.5” HDD
EVGA SuperNOVA NEX 750 B 750W

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All Answers

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Answer
Since it did go from 3700 to 4000
by R. Proffitt Forum moderator / June 18, 2015 6:39 PM PDT

It did try to compensate. Since it didn't work you need to talk to your machine's builder about how to correct this. Most common are better coolers and fans.

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More about this 125 Watt TDP CPU.
by R. Proffitt Forum moderator / June 18, 2015 7:03 PM PDT
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Answer
all that
by James Denison / June 18, 2015 6:46 PM PDT
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Bios
by DaylonRuS / June 18, 2015 8:45 PM PDT
In reply to: all that

I explained in the first paragraph that I have already tried that. The answer was to rewrite the bios, which apparently fixed something that updating and resetting the settings to default did not.

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on a high wattage CPU
by James Denison / June 18, 2015 9:03 PM PDT
In reply to: Bios

I don't mess with motherboard control, I just plug fan direct to power and let it run full all the time. On lower watt unit, the motherboard control is great for quiet and power saving.

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Answer
Get a better fan
by techno_original / June 18, 2015 8:17 PM PDT

Your system is now running load it didn't bargain for. The first thing I would recommend you doing is to change the fan and get a better one. The issue can simple means that now with a new OS and higher work load, the processor is working harder than before - thus emitting more heat which that fan cannot manage on cooling..... Once your processor surpasses a ceiling temperature , the PC will automatically shut down to prevent the processor from burning. The ARCTIC Freezer 7 Pro Rev 2 - 150 Watt Multi-compatible Low Noise CPU Cooler should be a better option.

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Or, this fan could just go the speed it's supposed to.
by DaylonRuS / June 18, 2015 8:41 PM PDT
In reply to: Get a better fan

As I explained in the post, the fan's speed was proportionate to the heat, but the ratios were incorrect. The fan is plenty capable of running it's CPU at 100%, regardless of which OS it's running. As I explained in the 3rd paragraph, previous stress tests could not cause it to shut down. Someone on another website suggested that I rewrite the bios, and this has fixed the problem. The fan is now running at a speed fast enough to keep the temperature around 110F at all times.

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Most folk just replace the HSF.
by R. Proffitt Forum moderator / June 18, 2015 9:24 PM PDT

But if you want to do a BIOS rewrite, good. Very few people I know can do that today. The last time I did that was about a decade ago.

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