Quote Originally Posted by unclewebb View Post
Just finished some very interesting testing tonight with the IR thermometer and I think I've uncovered the core temp mystery with these chips.

Absolute Temperature = TjMax - DTS

The value of TjMax is not publicly documented for any of the Intel desktop processors and there is no magic bit that any software can read to determine this value. That's why whenever a new chip comes out, CoreTemp takes a guess and some times gets it wrong. DTS is the value put out by the on chip digital thermal sensors and shows you how far the chip is from the throttling point.

The programmer of CoreTemp bumped TjMax up to 105C for the E8x00 desktop processors. TjMax=105C is fully documented by Intel for the mobile processors but I don't believe it applies to the desktop 45nm core duo processors. After numerous runs up to the throttling point, I'm convinced that TjMax=95C for the E8x00 desktop series. The maximum Tcase temperature has been bumped by approximately 10C between the early Conroe processors and the E8x00 so it makes sense that TjMax was also bumped from the original 85C to 95C but not to 105C.

The DTS in my E6400 provided very accurate absolute temperature readings based on TjMax=85C over a 35 degree range from 50C to 85C. The same is true for my E8400 but the 35 degree range is now from 60C to 95C. Below that range the actual temperature vs the DTS based temperature diverge by approximately 5C so at a DTS temp of 40C the actual was only about 35C. The E6400 would also diverge by about 5C at very low idle temps but it ended up reporting temps that were too low. I'm not sure if Intel has made a correction for the E8x00 or if the DTS is simply not accurate at low idle temps and has a margin of error of approximately +/- 5C at idle for all core processors.

You can't adjust TjMax using CoreTemp but the latest beta version of SpeedFan 4.34b38 is reading the 8x00 processors. It assumes that TjMax=100C so you have to go into Configure->Advanced and set the Temperature 1&2 offset to -5 and check the "remember it" box for both cores. This sets TjMax=95C. You will finally have some very accurate core temperature readings from 60C to the throttling point at 95C. These sensors were not designed or calibrated for reporting idle temps so some inaccuracy down low should be expected.

dropglock: If you are running at default MHz then an E8x00 will run stable well past 70C. If you are overclocking and are getting near the maximum then you will probably need to leave yourself at least 25C of headroom before the throttling point to maintain stability. Temperatures are only unimportant if you are Prime stable.
Is this a fact that i can count on? how sure are you on this?
it do make sense though.. and i like that my temps are 10c lower, now it as i said, makes sense is this a value that we "people" should go after from now on? or what do you say, nice find anyway

regards.