Comments on: Why does my C2D Macbook Pro fan run constantly?

Question: Why does my C2D Macbook Pro fan run constantly?

crazyray — Sun, 21 Oct 2007 22:19:15 -0800

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.

By: wackybrit

wackybrit — Sun, 21 Oct 2007 22:46:28 -0800

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).

By: spiderskull

spiderskull — Sun, 21 Oct 2007 22:51:38 -0800

Yeah, I agree with wackybrit -- it sounds like something is eating up your CPU, which is causing the heat.

By: now i'm piste

now i'm piste — Sun, 21 Oct 2007 22:56:32 -0800

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.

By: crazyray

crazyray — Sun, 21 Oct 2007 23:48:22 -0800

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.

By: pmbuko

pmbuko — Sun, 21 Oct 2007 23:56:49 -0800

(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.

By: Electrius

Electrius — Mon, 22 Oct 2007 01:07:45 -0800

Are you running in normal OS X, or under Windows with bootcamp?

By: roofus

roofus — Mon, 22 Oct 2007 01:15:54 -0800

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.

By: ReiToei

ReiToei — Mon, 22 Oct 2007 03:44:11 -0800

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.