Not sure what has happened, whether it’s physically broken or something went wrong with the software. So the machine overheats fairly quickly now. This is running Debian 11 (bullseye) and /proc/acpi/ibm/fan says:
status: enabled
speed: 0
level: auto
so I don’t know if the heat is being recognized. The CPU does clock down as it gets hotter. I’m not getting any type of overtemperature alerts though, and I haven’t found any place in the acpi tree to read the temperature. That’s annoying since there must be some sensors in there.
It looks like there is a program called “thinkfan” in trixie so I might try to upgrade the machine tomorrow. I can only do so much at a time before the box gets too hot.
Any help? Thanks.

Does the fan turn on when booting? Does your BIOS have any fan entries? Just check if the hardware’s broken and replace it.
I will try rebooting it but I don’t think the fan turned on. I have the impression replacing the fan on these machines is a huge pain, plus I’d have to get the replacement fan someplace, so the box would be out of action for a while if I have to do that. I do have another old thinkpad that I can migrate to if needed.
Right now I’m doing an apt upgrade so can’t reboot til that finishes. Thanks!
Update: I power cycled the box and the fan did turn on during boot, and in fact it’s still running. This is strange but at least for the moment, I guess the problem has solved itself. I noticed during shutdown, the screen filled with @ signs, which I’ve seen a few times before. I think this ancient box may have flaky hardware by now. Someday I’ll get something newer. Thanks for the help.
Added: oh yes I also found a bunch of thermal sensor files in the /sys tree. I haven’t looked into how to interpret them and I guess I’m ok for now.
I’m not familiar with this specific machine, but I’ve dealt with similar fan problems in 3 other machines (twice successfully (both Thinkpads) and once not (not a Thinkpad)) and I’d recommend you open up your machine and clean it, including opening up the fan itself, which is often not as hard as it sounds and saves you the trouble of having to find a replacement.
I own cats. Blowing out the fans is never enough… Tweezers!
Just to be clear, I really meant to disassemble the fan until you hold in your hand the plastic thing that rotates (at which point you can really clean it, and take the opportunity to add a drop of lubricant on the axle).
Mental note: Send monnier my next smoker owned PC if I want it cleaned properly.