As said, I think you make some unnecessary over simplifications
I am a Physicist and I have done a lot of customised heatsink installations attaching old Socket A heatsinks to things they were never designed to be connected to.
So I do know my stuff and I can tell you right now that your CPU is not in good thermal contact with your CPU cooler. Please forget your preceonceptions.
it's the CPU to heat up itself, and not the heatsink cooler.
Correct. The CPU is heating up an awful lot in your system because the CPU cooler is not in good thermal contact.
Vicotnik, you would seem to forget that any transfer speed is finite
The transfer of heat varies with temperature. The higher the temperature differential, the higher the rate of heat transfer. This is why if there is good thermal contact you would see a slow temperature rise whioch starts tailing off.
Moreover you also insist about the cooler size, but it's definitely less important than how a cooler work (and I would add how a specific CPU work): a truck can be a lot more powerful than a car, but it can't be as fast as that.
Irrelevant anaology with a car and a truck. F=ma has nothing to do with heat.
I have already stated how you work out the heat capacity of an object, the mass of the object is a term in it. With the Orochi you have a massive heat capacity. If it was no good at radiating the heat, that would be a different thing, it would take ages to heat up but carry on getting hotter. That is not happening. The Orochi does not heat up. Your CPU is not in good thermal contact with it.
on the cooler there's no sign of poor/inefficient thermal contact, or of any mechanical damages: you can't have a murder without the murder weapon.
It's thermal contact, nothing else. Whether or not you can see it or not is not important. You could always try switching back to another cooler (do you still have the Intel cooler?) just to see what happens.
I don't know what "scolding hot" means
It means hot enough to burn your skin. If the cooler was in good thermal contact (which it isn't) then it would be at the same temperature as the CPU itself. If the CPU is at 98C then the cooler would also be at 98C. It won't be. In fact I'll bet you my house that it isn't. It will be hovering around the ambient temperature inside the case, maybe around 30C.
I used the Orochi to cool an Intel X3220 (a Q6600 G0), oc'ed from 2.4 to 3.6GHz.
That CPU has a TDP of 105W, more than the 95W of the 2600K. It is therefore more than good enough to cool the 2600K, if it is in good thermal contact.
So again, it's not in good thermal contact. Are we now clear on that?
In terms of cause, I have know coolers that have not been in good contact where it is OK at idle and terrible at load. Uneven pressure across the core could be a reason if the cooler is not properly level on the core.
Things to try:
1. Check the temperature of the cooler during operation. 50C feels hot to the touch so if the cooler stays cool then it is in bad thermal contact.
2. Try with the case lying down flat so that the cooler isn't putting excessive moment on the CPU socket. The Orochi is very heavy and if the weight of the Orochi is the problem, this will resolve it.
3. Try with another CPU cooler like the standard Intel cooler. If it is still bad then the cause could be the heatspreader coming off the CPU itself.