Here's a quick lesson on thermodynamics:
The word "cooler" when used with regard to the thermal management system of the CPU is a bit of a misnomer. The heat sink and fan assembly isn't a "cooler" in the sense that it refrigerates the CPU; rather it is a heat exchanger; moving heat out of the CPU, into the heat sink, and from there out into the air.
One of the key facts here is that the heat exchanger cannot lower the temperature of the CPU lower than that of the outside air. If the air temp is 70F, then the CPU cannot be colder than 70F. If the air temp is 100F, then the CPU cannot be colder than 100F.
So the ambient air temperature really really matters when running one of these stress tests - especially in summer (if your room is not air-conditioned). If you compare numbers between a test run in a 70F room compared to a 100F room, the 100F room will run 30F hotter even when the computer is working perfectly.
Secondly, any time heat has to move from one medium to another there is an efficiency involved. You can think of the transition as a pipe, where a highly thermally conductive medium with a lot of surface area is a fat pipe, and an insulating medium with a little surface area is a narrow pipe.
The thermal compound used as the interface between the CPU die and the heat sink is intended to widen the pipe that heat flows through to get it out of the CPU and into the heat sink. The surface of the CPU die is not perfectly flat, nor is the surface of the bottom of the heat sink. The thermal compound fills in any gaps between the die and heat sink so the pipe is as wide as possible. If the thermal compound is incorrectly applied, then the pipe for heat out of the CPU is smaller than it could be and heat will be slower getting into the heat sink where it can be transferred to the outside air.
And of course, the amount of heat coming out of the heat sink and into the air is a function of how much air mass is flowing over the cooling fins (itself a function of how much air the fans can move and how plugged up the air flow channels are) and how good the heat sink is at moving heat into whatever air is flowing over it (a function of the surface area of the fins and how clean they are)
Because temperature is a measure of how much heat is in any given component, any restriction in the flow of heat from the CPU die, through the thermal paste into the heat sink, and from the heat sink into the ambient air, will show up as an elevated temperature.
So when the CPU appears to be running hot, the questions that need to be answered, in order, are:
1. What is the ambient air temperature? (which represents the lower bound on the CPU temp)
2. Are the cooling air filters plugged?
3. Are the fans running at full speed?
4. Are the cooling fins on the heat sink dirty?
5. Is the thermal paste properly applied?
DG
