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Core 2 Duo Tcase - Tjunction temperature difference problem

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June 3, 2007 3:55:15 AM

Hi All,
I'm seeing something strange with the relationship between my Tcase (as read from SpeedFan) and my Tjunction temperature; they don't match that's described in the (excellent) Core 2 Duo Temperature Guide, hereafter refereed to simply as "the guide". I've provided the data the guide asks for to do a temperature analysis and am hoping for some feedback from forum readers. Data and summary below.

VARIABLES:
Ambient = 24.9C throughout test
Chipset = NVIDIA 680i
C2D = E6700
CPU Cooler = Stock
Frequency = 2666 MHz (stock)
Load = TAT @ 100% load (both cores) for 10 minutes
Motherboard = ECS PN2 SLI2+ (V1.0)
Vcore = 1.29375 (set to manual in BIOS) (SpeedFan reports 1.26)
Case = NZXT Nemesis Elite (3 case fans: front and side intake, rear output).

NOTES:
1. Case has an internal system temperature monitor probe that I've got secured to the rear wall of the case. This read 31C when the CPU was idle, and the same when it was under TAT load.

2. All fans were set to manual, 100% in BIOS. I also installed the NVIDIA north bridge fan that comes with 680i mobos.

TEST RESULTS:
Idle Temps -
Tcase = 43C (as read from SpeedFan)
TJunction = Core 1: 48C | Core 2: 47C

After 10 minutes 100% load with TAT -
Tcase = 61C (as read from SpeedFan)
Tjunction = Core 1: 67C | Core 2: 65C

SUMMARY:
As you can see, my big problem is that my Tcase temp is always about 5C lower than my TJunction temp, but according to the guide, if should ALWAYS be ~15C lower. Based on not seeing the 15C difference between TCase and TJunction, I'd say that one of them needs an offset applied to it. Because Tcase is supposed to be ~1-15C hotter than ambient, and my Tcase is ~18C above ambient, I'd guess that it's the Tcase that needs an offset, and that that offset should be ~ -10C in order to bring Tcase to 15C less than TJunction.

What does everyone think of that? Two other questions:

1. Based on my chipset, etc, does anyone have an idea of what might be causing the erroneous temperature report (e.g. BIOS or something else)? Note that Tcase reads about the same in BIOS, NVIDIA nTune monitor, SpeedFan, and PCWizard 2007, give or take a degree or two.

2. Assuming I need an offset of ~ -10C for Tcase (to give it the expected 15C difference with TJunction), this would bring my idle temp to about 31C. Based on my variables, is this a decent idle temp for my machine?

3. How about my load temps? Are they reasonable (or will they be once an offset is applied)?

Thanks in advance for any responses. I'd really like to get a "warm fuzzy" about offsetting one of the temp readings before I start to OC my machine.

Regards,
Jeff
a b à CPUs
a b K Overclocking
June 3, 2007 5:10:41 AM

roadbeer69, nice work on your build, and with following the Guide. Tcase Idle is the key measurement which indicates BIOS accuracy. With respect to your Ambient and configuration, Tcase is inappropriately high, and requires a -10c Offset in SpeedFan, just as you suspected. Before proceeding with overclocking, I recommend that you replace the stock cooler, which is unable to sustain safe temperatures beyond 1.35 Vcore.

Hope this helps, and enjoy your rig,

Comp 8)
June 3, 2007 2:07:49 PM

Comp,

Thanks for the response and kind words. Also, thanks for doing the C2D Temp Guide in the first place! I'll set that -10C offset for Tcase in SpeedFan. I'll also look into getting a better cooler.

Regards,
Jeff
!