Well, my mac has been having problems on and off for about a year now.
The main problem is the Drive Bay fan (macs have 9 fans, for the PC people reading!) each fan has a sensor, and unfortunately the drive bay one is directly above the drives, so it reads the heat as hotter than what it really is, and to make matters worse, the location of the fan to cool the drives (and sensor) is located right against the drives, so the sensor never really cools down much, and the drives practically freeze.
The nerd forums all say basically the same thing… move the sensor (it is a small stamp-sized circuit board, taped inside the box) which I did a while back, and it fixed the problem for a while… until tonight.
Revving like crazy, fan was running at 4,000rpm, instead of it’s usual constant speed of 1,000rpm. I opened it up and checked for dust (nerds say that this is one major issue, and dusting inside the box every few months is critical for the 9 fans to operate)
No dust, still a high RPM on the fan (it was also reporting a drive bay temperature of 128 celsius, which it obviously wasn’t, as I had my hand in there, and it would have been 20-25 at most.
Apparently a new sensor is about $35US to get, and swap it over myself (or pay Apple about $100+) which I didn’t want to do at this point…
Easy fix? I used some typical Switch Cleaner Lubricant (or Contact Cleaner) for use on electrical components, and now, with nothing else done, the fan is back down to 1,000rpm and reporting 25 celsius!
so, if anyone else searches the same problem, I hope this helps! Contact Cleaner is designed for electrical components (unlike WD40!!) and will not ignite (unlike WD40!!!) or harm your electrical equipment (UNLIKE WD40!!!!!!) 😀
If you come across this issue, I recommend it, as no harm can be done, all it does is clean off any grease and filth that is on there (mine looked clean, and I dusted it first, which made no difference!) Spray both sides, and wait 10 seconds. Do not wipe it off, leave it on! 😀