Why does my C2D Macbook Pro fan run constantly?

October 21, 2007 10:19 PM

I have a 2.33 Core 2 Duo Macbook Pro 15 inch laptop. Recently, I have noticed that both fans on it constantly run at the maximum 6000 rpm's. The noise is driving me nuts, and the battery seems to run out much sooner. My question is in two parts: (1) would anything in the system logs help explain why this is happening? and (2) how can I make it stop?

Here are the steps that I have taken to try to diagnose the root cause:

(1) reset PMMU per these instuctions
(2) setup new blank user account to see if it was software related (it wasn't- the fans actually kick in at full blast even on the login screen)

Please help me understand what is causing this. The bootup temp is 106 degrees F, so I really do not think it is temperature related.

posted by crazyray to computers & internet (8 comments total)

Have you tried running Activity Monitor (it's in Applications or Applications/Utilities) and looking at CPU usage? That way you might find some sort of program you've installed that's booting up and sucking up CPU (a new user account will not necessarily rectify that).
posted by wackybrit at 10:46 PM on October 21, 2007

Yeah, I agree with wackybrit -- it sounds like something is eating up your CPU, which is causing the heat.
posted by spiderskull at 10:51 PM on October 21, 2007

To answer the first part of your question: I wouldn't poke around in Console when running Activity Monitor would show you any runaway processes as they're happening.

Since you're sure it's not software (as step 2 seems to corroborate), my guess would be a thermal sensor error. To address that, proceed as follows -

Run the provided diagnostic software (Apple Hardware Test) that came with your machine. It's on one of the two grey DVDs that most people ignore or lose. Failing that, take it to an Authorized Service Provider or make an appointment at an Apple Retail Store for diagnostics.
posted by now i'm piste at 10:56 PM on October 21, 2007

I use iStat Menus to watch all the temperatures as well as CPU utilization, and do not see any unusual spikes (my CPU cores are currently running at 3% and 5%, with GPU temp at 106, CPU temp at 115, Enclosure bottom 90F, and Memory bank at 131.

Do those data points indicate anything interesting? I assume because of the variance in temperatures the thermal sensors must be working. iStat menus also says Right Fan is at 5998 RMP and Left Fan is at 5996 RPM.
posted by crazyray at 11:48 PM on October 21, 2007

(1) Try booting in Safe mode by holding down the Shift key. If the fans run normally, then you know you have a software/OS issue that can likely be fixed with a reinstall (Archive & Install).

(2) If booting in Sage Mode doesn't make a difference, try holding down Option at bootup to load the boot volume picker screen. If the fans are run high, then you've got a hardware issue.
posted by pmbuko at 11:56 PM on October 21, 2007

Are you running in normal OS X, or under Windows with bootcamp?
posted by Electrius at 1:07 AM on October 22, 2007

I had this problem with my MacBook. Exactly as Wackybrit describes, shutting down a stray process in Activity Monitor solved it. Subsequently though, when I sent my MacBook in for service, the engineers changed the heatsink unit, and now it all runs much cooler. The various software hacks available never made any appreciable difference to the fans.
posted by roofus at 1:15 AM on October 22, 2007

Have you tried a complete reinstall of the OS? This would be the only real way to confirm whether or not it's a software issue or a fried sensor.
posted by ReiToei at 3:44 AM on October 22, 2007