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So crack your head on this one. I'm not a noob, and this is the 6th computer I've built in the past 3 years.

Antec 900 Case
600w Xtreme Corsair PSU
DDR2 800 2x1gig ram

intel 6850 at stock speed 3.0ghertz

Zerotherm CF800 CPU fan/heatsink 

Asus p5n-em HDMI micro atx board

8800GTS 320mb
 

WD 37gig raptor hd / Seagate 250gig hd

Windows XP home premium 32bit

Basically, I've had a bunch of mic feedback issues and lost-monitor-signal problems with this setup the first two weeks I got it up and running, but I fixed them. I'm still stuck on this one though: the CPU idles at 38C and loads up to 49C when I lay the rig on it's side. When I stand the case up, the CPU starts from 39C idle and within 10 minutes it goes all the way up to 90C (thats when I decide to not see how much further it'll go and cut the power). Right now I'm using it as a footrest under my pc table, but I'm going to have to get it working properly aka rightside up. Airflow is NOT and issue. My antec900 creates tornadoes both up and sideways, and there makes no difference in the change of positioning for airflow. It's not the thermal paste. I've reapplied thermal compound Arctic Silver 5 (yes, not too much, not too little, grain of rice worth, yes yes). When I touch the heatsink when the CPU shows idling at up to 90C, it's definitely not burning like 90C should, but it is relatively hotter than laying down idle and load.

 In the end, I find it obvious the problem has to do with gravity. The thermal paste is on fine and the zerotherm heatsink is backplate-screwed on TIGHT. I can't even make it budge in any more after I figured it was gravity and screwed it in tighter. It is interesting to note that my Zerotherm CF800 idles fanspeeds at 764RPM and is supposed to have a heatsensor that ups the RPM when the temp goes up; however, the at 90C, the fan was still idling at 764RPM. In fact, it has never gone past any other RPM, even when its stable lying on it's side on loads (cpu fan sensor problem?). This is an issue, but I don't see how this can be the direct cause of the drastic differences in CPU temps when lying on side vs rightside up. I don't know what else I should be mentioning...

 My deductions lead me to believe it could either be something weird going on with the Zerotherm cpu fan though I wouldn't be able to succinctly hypothesize in any relation. I do have an Intel stock cpu fan/heatsink that I'll try if I don't get any clues here, but damn I hate those clip ons!!

It could be the motherboard, possibly the CPU latch/socket part has a loose piece or something.

 I'm basing this on my deductions that lead gravity to be the primary culprit.

Any takes? Remember, the only difference is if my case is laying on it's side, its fine. If its rightside up it heats my cpu out of control.

I forgot to clarify/mention that when it's rightside up, the CPU starts off at 39C and automatically goes up to 90C incrementally by itself. I don't do ANYTHING, windows just starts up, and I leave it alone. No open windows, task bar usage, nothing. I just turn the pc on and leave it.

Is this mobo readings? If so download real temp and see what the cores show. As may be mobo sensor. Post back results.

http://www.techpowerup.com/realtemp/

As Lowboy asked where or what software are you getting these readings from, have you tried other temperature programs such as Speedfan, CPUZ or any of the others out there. Now another possibility have you checked your BIOS for settings on the fan speed or what the temp readings are there? Get back to us with this info and we will be more than happy to help you out as best we can.

When you stand it up, does the fan keep turning?

Does the main board flex any when you stand it upright? Have you tried picking up on the heatsink while its upright to see if it is?

If it warps the main board much it might pull away from the CPU.

 

 

My shot in the dark

I had the same problem with my computer, that the cpu heatsink would jump to high temperatures really quickly. Can you check if one of the legs is damaged because that can cause the temperatures to go high. If you do see any damages, or awkward positions when the heatsink is upright you might have to purchase a new heatsink and re-apply it to the computer.

 If you have another heatsink or a computer, you can either put the new heatsink in the computer or get another heatsink and put it on the current computer to see whether or not the heatsink is the problem. If the heatsink works fine, then it could be something else.

Another shot in the Dark, Something simple, Top Mounting Screws (HSF)?  Snug?  If not maybe gravity pulls HSF away fron CPU? Is anytihing touching Fan when it's Upright? System will Auto Shutdown when it gets that Hot. Just for **its and Giggles, lay PC on its side and pull up on HSF. No Movement? Grasping at Straws, Upright, go into setup and Monitor Temps before Windows Loads up. All else fails, try stock HSF. Could try removing HSF and reinstall. Stumped.

 

CrazyCraig:

Another shot in the Dark, Something simple, Top Mounting Screws (HSF)?  Snug?  If not maybe gravity pulls HSF away fron CPU? Is anytihing touching Fan when it's Upright? System will Auto Shutdown when it gets that Hot. Just for **its and Giggles, lay PC on its side and pull up on HSF. No Movement? Grasping at Straws, Upright, go into setup and Monitor Temps before Windows Loads up. All else fails, try stock HSF. Could try removing HSF and reinstall. Stumped.

 I agree, you should try checking if the heatsink is away from the cpu. If it is, it could be a problem.