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Strange CPU temps / fan speeds at idle on i5-2405S / DH67BL

New Contributor I

I have a system with a i5-2405S, DH67BL, and the original Intel CPU fan, running Windows 7 Pro. Up until recently the fan speeds were as expected, hovering around 1000 RPM, and the CPU temps pretty much staying in the high 20s at idle.

I don't always use Desktop Utilities, so I really do not know when this started, but yesterday the CPU temps ranged from 25 to 44 at idle, yet the fan stayed around 1000 RPM. I wondered if the thermal compound needed a refresh, so I removed the heatsink/fan and reattached it using Arctic Silver to achieve the best efficiency. I have built enough PCs to know how to apply thermal compound and I tried to make this application perfect.

Nothing has really changed. I watched Desktop Utilities for ten minutes and the temps seemed to be a little lower on average, but they still ranged into the 40s once or twice on idle. And the fan continued to hover around 1000 RPM.

I have three questions.

First, how is CPU temp determined? I assume it is calculated via a diode built into the CPU, but maybe there is a diode in the motherboard directly under the CPU socket.

Second, what is the maximum speed or speed range of the factory Intel LGA 1155 fan?

And third, if Desktop Utilities and the fan-speed control use the same values, then why doesn't the fan speed up when the CPU temp rises into the 40s and stays there for a minute? Or does the fan-speed control have some way of knowing when a CPU temp is bogus?

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6 Replies
Community Manager


Here are the answers to your questions:

1. CPU temperature is determined by the processor's work and load. The regular maximum operating temperature is 69.1°C (Tcase) which must not exceed 70 °C: ARK | Intel&# 174; Core™ i5-2405S Processor (6M Cache, up to 3.30 GHz)

2. A factory Intel fan speed should be between 1700 and 4000 rpm.

3. Could be a software issue with the utility; make sure you have the latest version of the Intel(R) Desktop Utilities: Download Center

We also recommend checking the processor temperature and fan rpm's in the BIOS to confirm. Fan speed is determined by the processor and motherboard so the issue could be also related to a defective fan header.

New Contributor I

1) I looked at the Technical Product Specification and it stated that the "Thermal diode [is] located on the processor die." So if the CPU is not actually running like crazy, the diode on the motherboard is probably half-dead.

2) I have never seen an Intel fan turning at anything other than 1000 RPM (or thereabouts) at idle on a i5 CPU, but then again, I have only built a handfull of PCs, all i5-based.

3) This is a dual-boot machine with 8 on one disk and XP/7 on a separate disk. 8 is a new install and I just loaded Desktop Utilities from after filtering on DH67BL and then OS.

I am running that PC right now and monitoring temps in BIOS. CPU idle temp is 55, even higher than I saw before. PCH idle temp is 46, three degrees higher than I usually see on Intel boards. The fan is turning at 1000 RPM. The case is a three fan model, with the 120mm front, 120mm side, and 92mm rear running full-blast because they are connected directly to the PSU (in other words, airflow is not the problem). I visually inspected all four fans; they are all turning.

Given the high indicated temps, I do not understand why the CPU fan is not turning faster.

Community Manager

I have the same issue on DQ77KB / i3-3220T and Akasa AK-CCE-7106HP cooler.

Temp in stress is over 72 and fan speed only 700RPM (same as idle).

I can modify in BIOS min RPM fan speed (default is about 20%) but it results only faster turning (constant - irrespective to the temperature) :/

New Contributor I

So it appears to be a firmware issue. At 72 degrees, the fan should be spinning its fastest. Mine just started this behavior recently Was your board always this way?

On my other two PCs, I have a 3-pin CPU fan attached to the fan header and so the fan always runs at its top speed. From now on I think I will avoid PWM fans and always use 3-pin ones to achieve a fast, albeit constant, flow of air.

Community Manager

This is new motherboard with previously released 0046 (screw up) bios - for me this board always this way


PS. What happens to the Intel MOBOs software is crying to heaven for vengeance (the problem is chasing a problem)


Ok, let me answer these questions properly...

1. Intel processors have not used diode-based temperature measurement for many generations (the Intel(R) Core(TM) 2 Duo was the last that did so). Temperatures are (now) measured using Digital Thermal Sensors (DTS). There is a DTS located at the hotspot of each and every processor Core. There may also be DTS at other hotspots, such as within the memory controller or graphics cores. These DTS are used not only to report temperatures, but also to support such features as the Thermal Control Circuit (TCC), which protects the processor from catastrophic overheating, and Intel(R) Turbo Boost Technology. The processor exposes a single temperature, an amalgam of the temperatures from all of the DTS incuded, to external monitoring and fan speed control devices. This is done via a single-wire bus known as the Platform Environmental Control Interface (PECI). It also publishes a temperature threshold, called Tcontrol, that tells the fan speed control device what temperature it is to maintain (stay below).

2. The specifications for the boxed processor heatsink-fan units can vary from one processor to another. In general, the fans have an absolute minimum speed of 1000RPM.

3. The fan speed control solution on the 6 and 7 Series motherboards implements a temperature control range that is 15 degrees wide. The upper limit of this control range is known as the Control Temperature. In the case of the processor, by default, the Control Temperature is set to the processor's Tcontrol temperature (you have the ability to lower the Control Temperature, if you wish, from within BIOS Setup (or Visual BIOS if available) and/or with Intel(R) Integrator Toolkit). Operationally, if the temperature is at or above the upper limit for the control range (i.e. above the Control Temperature), the associated fan is operated at its maximum speed. If the temperature is at or below the low end of the control range, the associated fan is operated at its minimum speed. Across the control range, the speed is increased from its minimum to its maximum, following some chosen curve. The shape of this curve is controlled using the Temperature Responsiveness parameter. I have a picture that shows the shapes of the curves, but I can't seem to get this editor to let me insert it. I will have to provide later...

Let's look at an example. Most processors have a Tcontrol temperature that is somewhere between 80 and 90 degrees (there are exceptions in both directions, however). Let's suppose it's 80 for our example. What this means is that, below 65 degrees, the fan is going to be sitting at its minimum speed all the time. Let's respond to this like a FAQ:

Q. Why, when my processor temperature goes from somewhere in the 30's to somewhere in the 40's, I don't see the fan respond?

A. For our example CPU, you are not going to see any response until the temperature reaches 65 degrees.

Q. Why does it wait until the temperature is so high before responding?

A. Because, quite simply, it doesn't need to. This isn't really a high temperature Your processor could sit at its Tcontrol temperature for is entire warranted lifetime and it would not suffer any degradation due to thermals. There is obviously a need to stay below this level to ensure headroom for Intel(R) Turbo Boost Technology, however. The 15 degree control range provides this headroom...

Q. What if I want it to stay cooler?

A. You have the option of using a lower Control Temperature. You can change it in BIOS Setup (or Visual BIOS) and from Intel(R) Integrator Toolkit.

Q. I watched the fan response and saw variations in the fan speed that your explanation doesn't cover...

A. Yes, absolutely true, I dumbed down my answer to make it easier to explain. In fact, you can have two temperatures associated with each fan controller and the fan controller will respond to the temperature that requires the higher fan response. You choose the temperatures using the Primary and Secondary Temperature parameters for each fan controller. By default, for most boards, both the Processor and VR temperatures are associated with the processor fan controller and both the PCH and Memory temperatures are associated with the chassis fan controllers.

Q. I still see some variations in the processor fan that your explanation doesn't cover.

A. Yes, the processor heatsink-fan unit also has a temperature sensor in its fan hub and it will automatically speed up the fan if the temperature of the air coming into the fan gets hotter (the thresholds vary from fan to fan here too).