Wild guess, but have you used me_cleaner at any point? This happened to my T510 when I tried neutering the Intel ME, sometimes the fan works, sometimes it wouldn't, and no apparent errors came up.
ThinkPad
IBM and Lenovo ThinkPad laptop enthusiasts!
No I've never used me_cleaner. Maybe I should. It's possible that the fan got stuck and disabled itself but later the obstruction cleared. I did notice some noise from it, and it's spinning quietly now.
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!
maybe there's too much dust that the fan can't spin? i have a w520 and the fan on it is very loud, very hard to not notice if it ever spins.
It's sort of weird, ACPI said the fan was enabled and not spinning. I would have expected different if it was trying to spin. After the power cycle it sounded about normal. But I'll try to clean it, at least with compressed air. Thanks.
btw i recommend against compressed air, laptop fans are fragile and especially on this 15yo machine. it's very possible to break the fan blades. imo a soft brush is better.
Hmm interesting, thanks, yikes. I will avoid the compressed air then, or stay with very low velocity like a blower brush. But, I had hoped to avoid disassembling the machine. Wow. I powered it off last night and turned it on a little while ago and the fan is running gently.
the t/w520 isn't that bad to disassemble, it's all very easy after you manage to detach the plastic palmrest held with clips. if it runs well now that's great :)