4 Replies Latest reply: Apr 26, 2009 6:27 AM by suckerpunch86
Graek Level 1 Level 1 (85 points)
I have OS 10.5. Yesterday I downloaded and installed several updates from Software Update. Since them my computer is running REALLY hot and the fan is constantly racing. I'm not doing anything different or using any new apps. I have Mail, FF and NeoOffice running and the moment and my fan is running at 5200rpm and my CPU is at 67-70 deg. I looked at activity monitor and its not showing anything out of the ordinary.

Today it got weirder. So, my battery had bitten the dust 3 or so months ago. I bought a new one today. I took the old one out, and restarted the computer with no battery in it. I used it for an hour and the CPU temp stayed under 60 and the fans at a nice 2000rpm! Was this old battery somehow the problem?

So, I shut down, put the new battery in and within 5 minutes the CPU temp was up to 71 deg and the fans at 3400 and holding.

So, computer on (I hope this is ok), I popped the battery out. INSTANTLY, the temp started dropping and the fans slowing. Within a minute I was back down to a temp of 60 deg and fans at 2002 rpm. Within several minutes I was down to 52 deg for the CPU and 1999 rpm on the fans.

Again ... popper the "new" battery back in within seconds the CPUs temp started going up. Within 1 minute the CPU temp went from 52 deg to 70 deg. And aagin, pop the battery out and the temp drops instantly and dramatically (same behavior using the new and old battery.)

Ideas?!?!?!?


(Note, my last battery failed under mysterious circumstances ... if went from holding 2 hours of charge to only 20 minutes overnight, with the only change being me upgrading from 10.4 to 10.5. (and the battery indicator being totally off. Many many people here are posting these same battery issues...random shutdown when battery shows 80% charge, etc.)

MacBook Pro 15" 2.2GHz Intel, Mac OS X (10.5.5), 2 GB RAM, 160GB HD, Super Drive
  • 1. Re: CPU HOT & fans race when battery in, runs normal with battery out
    Graek Level 1 Level 1 (85 points)
    Problem solved, but it' still weird. I was searching the forums here for an answer and started reading one on unusually high CPU usage ... which would explain a really hot processor. I checked Activity Monitor before, but didn't realize I was only viewing My Processes and not All Process. I checked All Processes and sure enough there was an app PrintJobMgr that was using 99+% of my CPU all the time. See thread for full details: http://discussions.apple.com/thread.jspa?messageID=8827047&#8827047

    So, I killed the process and not everything is running fine.

    What I still can't figure out is what, how and why removing the battery cooled the processor and thus slowed the fans. This makes no sense, yet it was completely reproducible behavior.

    Oh well. Solved.
  • 2. Re: CPU HOT & fans race when battery in, runs normal with battery out
    macinatic89 Level 1 Level 1 (0 points)
    I experienced a similar problem today. I was calibrating my battery which I do about every 2 months. I let my computer run on battery power until it went to sleep by itself. Afterward I plugged in the power cable and turned the Macbook Pro back on. With only a few processes running and temperatures very normal, the fans started racing up to like 6000 rpm. I restarted the computer and that didn't solve anything. I took the dead/charging battery out and powered the computer on (using the power adapter) and the fans immediately slowed to 2000 RPM (normal). I put the battery back in and the fans started speeding up immediately. Removing the battery once more fixes the fan racing problem.
    Anyone have any ideas why this is? Does charging a completely dead battery actually require the fans to run like that?
  • 3. Re: CPU HOT & fans race when battery in, runs normal with battery out
    neuroanatomist Level 7 Level 7 (31,690 points)
    Graek wrote:
    What I still can't figure out is what, how and why removing the battery cooled the processor and thus slowed the fans. This makes no sense, yet it was completely reproducible behavior.


    It's by design - the CPU will sometimes (for brief periods) require more power than the AC adapter can provide, and the additional power is drawn from the battery; with the battery removed, the OS throttles back the CPU to avoid this situation.

    http://support.apple.com/kb/HT2332
  • 4. Re: CPU HOT & fans race when battery in, runs normal with battery out
    suckerpunch86 Level 1 Level 1 (0 points)
    Even I suffer from the same thing, and I have two batteries that I use. I would agree that the increase power demands throttle the CPU but then it cools down when it reaches around 70%+ charge.