I just tried the stock Intel Cooler on my Q9300 again............and real temp reports core temps of 49/47/43/48 at idle. I used AS5 too. Its night and nice and cooled down in here and all case fans are on 100%. My HDT-S1283 doesn't do any better except with running Prime95 small FFTs. The core temps while running Small FFTs went up to 90 C in just a few seconds. That is ridiculous. I am going to order the bolt-thru kit in the next few days and try it out with my HDT Cooler. Nothing that I do seems to work. I need any suggestions that you might have for me.

try lowering the Voltage, most cpus can run at a lower vcore than the one they ship with

Lowering the core voltage is only a partial remedy, but a great idea for anyone to do. I was able to get my Q9450 down to 1.8 volts at stock speed and was 100% stable under long term full load (video editing).
Never thought it would run stable like that, but it was pretty neat, and it ran about 5c cooler, too.
Anyways, either there is too much thermal paste being used, not enough paste, or you do indeed meed to upgrade the mounting hardware to the backplate method to see if that helps.

Good luck to you!

What voltage should I most likely try? Or just keep lowering it until I get the best temps? And also I just tried reducing the Clock to 266x6 Multiplier and it was the EXACT SAME TEMPS......I seriously don't get it. It seems more likely that the DTS are faulty (as common in most 45nm procs) than the Cooler. Because I get the same temps almost with the stock or the S1283. But I gotta try what shoota said.

I really hope you mean 1.18 or 1.08V, because at 1.8V, your Q9450 will be toast any time now.

@OP: You may want to also consider using Real Temp instead, and also read the interesting documentation and explanation of inaccurate temperatures on 45nm Intels:
http://www.techpowerup.com/realtemp/docs.php

Those idle temps look like they are really just miscalibrated. Try touching the heatsink - it's probably cool. What are load temps (Prime95 torture test) like?

Yikes!!!
Yes: 1.18v...

Too little sleep, yeah, that's the ticket... ;-)

^ seriously

lol. i was thinking, ur Q9450 can go up to 1.8v without frying? O_O

Wait a sec........zipz0p? You should re-read my post. I am using Real Temp and it goes to about 90 C in full load under prime95s Small FFTs test. I just lowered the voltage to 1.125v in BIOS and it might of made a 1-2 degree difference but I'm not sure. Is it possible that it could be too low of a voltage?

wat is the TjMax for the Q9300? Real Temps has it by default set to 95.

90C is too high of temps in any circumstances...

seriously check your HSF if you installed it correctly...

if anything, can u still RMA your Q9300? i would RMA it if u still can, i'm sure its not pleasant to see your CPU at 90C in Prime.

If it idles in the mid 40s, and goes to 90 while working, it sounds like the heatsink isn't attached properly. (or the thermal paste isn't right.)

Take the motherboard out of the case, and put the heatsink on then. Don't forget to apply the correct amount of TIM. It might seems like a PITA to take the motherboard out, but it really is the best way.

But aznguy0028...do you think that it is a HSF problem or a proc problem? The 90 C is only with the stock cooler. it gets in the high 50s with the Xigmatek. But even 50 C at stock on full load is still too hot.

And I only got the Q9300 2 weeks ago. And how does RMA work? I also might try and use less paste and see.

EDIT: I really would not have to take the Mobo out if I don't need to, but if I have to I would. I don't understand how the Stock Intel Cooler could not be attached right cuz its pretty simple.

Sorry abouto that jman. I definitely didn't read that carefully enough. Not enough sleep

90C at load is wayyyy too hot. But 50C at full load with the Xigmatec isn't necessarily too hot, that sounds fine. I get up to almost 60C full load with a similar cooler at 3.2GHz on my Q9450. Depending on the program I use, my idle temp is listed around 20C, 30C or 40C.

Pushpins suck

oh, you were using a stock cooler? .....i see

high 50's is fine under 100% load. that is completely safe.

most people would agree with me that you should stay below 70 on full load...i try to stay 65 or under. but 70 seems to be a point that most people agree on here.

my Q9450 goes to around 58-61 on full load in Prime95 too, its no big deal. the place where i live is 100+ everyday during the summer.

i don't think you should have too much to worry about, post more info if anything else troubles you, im sure people on this forum will be able to help, myself included.

since you have the Xiggy, it is highly recommended that you get the bolt through kit, much better contact w/the CPU.