The RAM slot was closer on the bottom, so I was thinking it would be easiest to go there (e.g. machine a copper ram slot cover with ribs - dreaming of course, not happening any time soon), but not sure if that would actually work well enough since there's no airflow except passive.
FWIW, the hot region under the T43's touchpad seems to rely on passive cooling through the bottom too. There's something looking suspiciously like a thermal pad visible through one of the holes in the bottom, and blocking that area (e.g., by placing it on your lap) raises temperatures be 3-4 degrees pretty quickly.
Re: crappy fan control above, this is why I'm very interested in mg's thread on the EC and your suggestion to look into whether the fan is directly PWM controlled from the EC (and that it might be "editable")..
We know it *can* be done in software control for some older models. But it was removed in later model's firmware. See the ibm_acpi patches posted to the linux-thinkpad list recently, they encode this knowledge.
Advantages: No externally visible modding. No hot radiating surfaces on your lap. Unaffected by other hot components.
What do you mean by unaffected by other hot components? Couldn't read from context..
There was this other thread here about binding the chipset to the CPU or GPU heatsink. That's great for idle, but when the CPU heats up under 100% CPU it will carry the chipset with it, perhaps out of comfortable range (the CPU is rated higher than the chipset, and better isolated from your lap). This effect is very visible with the CPU and GPU on the T43, which share a common fan radiator -- once things stabilize they're never more than a few degrees apart, even if one is idle and the other going full throttle.
True, though not totally in my case -- the CPU is the hottest, but the power supply thmal sensor especially as well as the Northbridge thmal sensor also get pretty cooking. And the problem is that when the CPU is done it cools down in 2 seconds thanks to the heatsink, while the fan keeps going at full blast while the other two cool on their own with a sloow time constant - because the fan is trying to cool but has no impact.
Evidently, the ThinkPad's engineers cared very little about minimizing fan action. The goal was apparently to prevent hardware failures and safety hazards. A constant moderately high temperature, and continuously on fan, weren't a concern.