Why does my 12" Powerbook overheat so much?

June 8, 2008 12:36 PM

Why does my 12" Powerbook overheat so much?

I recently bought a used 12" Powerbook G4, the 1.5 GHz model. It was in great physical shape when I bought it, so I have no reason to believe the previous owner was anything but kind to it. Immediately after buying it I ordered a new battery (previous owner had not taken advantage of the G4 battery recall), maxed out the RAM to 1.25 GB and replaced the internal 80 GB hard drive with a 160 GB drive (5400 RPM, Hitachi Travelstar).

Now the processor seems to overheat with annoying frequency. Normally -- like right now, when I have a half-dozen apps open but am not really doing anything intensive -- it hovers at around 45-50 deg C. But certain things seems to throw it into absolute fits, with a fairly rapid climb in temp often resulting in an emergency sleep when it hits about 80 deg C. The fan kicks in like crazy but that doesn't seem to help at all. It happens when I watch streaming video (Youtube, etc.) and when I am downloading large files from fast servers (Apple/MS/Adobe software updates, etc.). Doesn't seem to have a problem copying large files from one local drive to another.

I can't seem to remember having any of these problems before all the upgrades I put in. Is it possible that I, e.g., didn't tighten some screw properly before putting the computer back together again, and now the heatsink isn't doing its thing properly? Could the new RAM, hard drive or battery have anything to do with it? Strangely enough it's the processor that's overheating, which I didn't touch. And the battery is on the other side of the chassis, so I don't think that's it. The closest thing to the processor, I think, is the hard drive, but that never seems to exceed its specified upper limit of 59 deg C.

One final thing: I lost the little screws holding on the RAM door in place on the bottom of the laptop and used some scotch tape instead. As a result, the RAM door is maybe 1 mm lower than it should be, i.e., not flush with the bottom of the case. Could this be possibly messing up some super-delicate airflow thing on the underside of the case?

Help! I love love love this computer in every other way. And I'm trying to make it my main work machine, so I can't really have it doing this.

posted by DLWM to computers & internet (11 answers total)

I doubt it's the RAM door messing things up - airflow, even in laptops, isn't delicate or tuned enough for that to make a difference. If I had to guess, I'd say that the new drive is the culprit. You may not be seeing anything over the upper temperature limit on the drive because it's shedding heat onto the processor - so the processor gets overheated because the drive cooling is doing what it's supposed to.

I'd guess that the original drive was a 4200 RPM unit, which would generate quite a bit less heat.
posted by Dipsomaniac at 12:45 PM on June 8, 2008

Apples have trouble playing flash. My previous question. It's annoying, and loud, but you can't fix it.
posted by SeizeTheDay at 12:47 PM on June 8, 2008

Notebook heat budgets are pretty tight. More RAM means more heat.

A new hard drive that runs moderately hotter than what it replaced can put the system into maximum cooling mode more often.

Alternately, it's possible that the CPU's heat sink is loose, or that there's an obstructed vent.
posted by zippy at 1:11 PM on June 8, 2008

Look at your active processes. I recently got a PowerBook too and noticed that cron was driving the processor into overtime, overheating the machine. I have not tried reinstalling Mac OS X yet, maybe you ought to give that a go if you can? I know it is not any replacement parts as the one I got has had not ever been to be fixed and has the same problem.
posted by ooklala at 1:16 PM on June 8, 2008

I just ran a test on a 12" PB that I have here (1.5 GHz, 768 MB RAM, original 60 G drive). I loaded up two windows showing Youtube to peg the processor at 100% and also started a Disk Utility process to create a new disk image out of the Applications folder, to get the disk rocking at the same time. The temp at the bottom of the CPU is holding at 57 Celsius and the fan is running at around 4500 RPM.

Surprisingly (to me, anyway) the drive is a 5400 RPM unit, but there's a good chance your drive is generating more heat. It may also be a problem with less than optimal cooling at the CPU combined with more heat production due to the upgrades.
posted by Dipsomaniac at 1:19 PM on June 8, 2008

That's not a 2-fan machine is it? My MB Pro had an issue where only one fan was spinning. Apple store fixed it up no problem, but make sure that that isn't the issue. Since you can hear a fan so loudly, it could easily not occur to you that one isn't spinning at all....
posted by John Kenneth Fisher at 2:02 PM on June 8, 2008

iFixit.com shows only one fan on the 12" machine, on the CPU itself. There's always the possibility that the intake and/or vent for the fan are blocked up, which would explain why the fan doesn't seem to be having much effect.

You could try blowing some canned air into the intake (around the back, under the screen hinge) or the vent, on the left hand side at the front. If you do that, be VERY careful not to just blast air in there at full speed - you'd run the risk of spinning the CPU fan up to the point of damage.

Depending on your level of comfort, iFixit.com has disassembly guides that may let you have a look at the air path to see if it's blocked. The 12" PB looks like you'd have to take the keyboard off to do anything, though.
posted by Dipsomaniac at 2:32 PM on June 8, 2008

Some people say that Apple’s manufacturing process is a little too generous with the thermal paste between the cpu and heat sink. (That is, too much paste actually reduces its effectiveness in conducting heat.) They say to remove the sink, scrape off the paste, and reapply it. YMMV.

I will also attest to the fact that the Flash plugin often consumes excessive cpu and causes the fan to kick in on my ’Books, too.
posted by ijoshua at 3:10 PM on June 8, 2008

Flash is indeed slow and a processor hog on PPC macs. If you want to maximize CPU for a while on this laptop, watching youtube videos should do it...

I used to own the 1GHz model of this laptop, and while I never had problems with overheating, it did seem to heat up quickly regardless of the fan turning on, at least compared to the four other apple laptops I've owned. I'm no real hardware guy, but I'd guess that Apple was pushing the thermal design of the 12" Powerbook a bit more than it normally would.

I doubt that the extra RAM is the source of the problem, IIRC the RAM slot is on the bottom of the logic board, in no position to imped air flow. Likewise for the battery, I'd guess.

You say the hard drive isn't heating up, but I'd check anyway to make sure the thermal profile of the drive is no higher than the original drive's.

My wild guess at your problem is that the fan is a little worn, the inards are dusty, and/or the thermal paste on the heat sinks is or always was not quite right. The reason why you didn't see this before is that without the new RAM, swapping was slowing the whole works down enough that you never saw the demands of full performance.
posted by jacobbarssbailey at 4:49 AM on June 9, 2008

Thanks for the helpful responses, everyone! When I don't have any pressing work that requires me to use my laptop (a very likely scenario, heh) I'll try taking it apart and seeing what the deal is with the airflow and heatsink screws.

I'm fine with taking the machine apart and have done it before, but I have to confess the notion of removing the heatsink from the processor, scraping off the thermal paste and reapplying it sounds rather daunting.

I think I'll try booting off an external FW drive, doing something drive-intensive and seeing if the processor still heats up. If not, then I think Dipsomaniac's may be the best explanation. The original drive was also a 5400 RPM unit, but I think it was made by a different manufacturer, so who knows.

Thanks again!
posted by DLWM at 7:37 AM on June 9, 2008

The 12" powerbook does not use normal thermal paste. They use several thermal pads, two of which are sorta like a rubbery foam material. The other is a pad that loosly resembles thermal paste but does not come in a tube and cannot be overapplied.. The reports of apple using too much thermal paste started with the macbook and have been made only by people who have no idea what they're talking about.

These machines are not known for having heat issues. I've worked on hundreds of them. Seems the most likely scenarios are:


1. In a previous life the computer's heatsink was removed and whoever did the repair neglected to install any thermal pads (or they just got their greasy paws all over them, making it impossible for them to properly transfer heat).

2. New hard drive runs too hot. Though if this was the case you'd most likely notice that the left side of the computer, just below the keyboard, gets so hot you can't touch it.

3. Perhaps you're using the computer on a pillow, your lap, blanket, or something else which prevents airflow from moving under the case. While I think it is ridiculous, Apple would you like you to know that your powerbook is NOT a laptop. It is a portable computer, intended to be used on a flat surface. If you use it on your lap you might get burned or it might overheat... but don't blame them, they told you not to use it on your lap.

I think that #1 is the most likely. As I said, these are not machines known for overheating so I think something is definitely wrong. Your hard drive is unlikely to generate enough heat to shut down the machine. And the missing screws over the RAM plate definitely would not cause any heat issues.
posted by J-Garr at 1:09 PM on June 9, 2008