I'm using SpeedFan to control my laptop temperature. Among the readings for outright local CPU, GPU, HDD, DIMM, Core, and ACPI temperature, there is an unknown reading marked "Temp4". The temperature of the reading seems to match the highest temperature of the other readings at any given time when my main fan is off (Say, if the CPU is running hottest of all readings at 40C, temp4 reads about 40C as well. If the GPU spikes up and surpasses the CPU temp to, say, 65C, the Temp4 reading jumps up to match the GPU reading of 65C.). When my main fan begins to run at full speed, Temp4 will drop to around 3 to 6 degress lower than the highest temperature shown by all other readings, staying that way until it reaches room temp, at which point it stops getting any cooler. Since the cooling system in my laptop uses a heat-sink that leads to a single main fan and vent (As do the cooling systems in most laptops), it got me wondering: Do the fins, or the heat-sink near the main fan, have a temperature sensor in it in addition to the temperature readings for each specific system/ chip set? If so, could the Temp4 reading be for the heat-sink?
If the heat-sink does in fact have it's own temperature sensor, it would make sense why the system-regulated fan settings don't seem to engage the fan according to any individual temperature reading; my fan will engage much faster (Almost three times as fast) with all my sensors running at 45C, than with any one single sensor reading 65C. My thoughts are that the system would be letting the heat-sink absorb heat until its temperature has risen past a preset value, as running the main fan when the heatsink is still cool- and can still absorb more heat from the chip sets- would seem inefficient as I don't believe it would serve to directly cool the hot systems until the heat has traveled to the main fan, anyways.