Cleaning the fans and vents of an older rMBP can really help

[klagermkii]

I've had my 2012 Retina MacBook Pro for just over three years now and have been noticing some weird slowdowns in the past few months, especially if I was running a VM. At first I was blaming it on Parallels or El Capitan, but then was noticing it happened with other CPU taxing apps. If one did any kind of sustained load on the machine the fans would ramp up and the machine would get slower and slower with kernel_task taking a larger and larger percentage of CPU time. It didn't even have to be a heavy load, just something that was a constant drag on the machine.

Downloaded Intel Power Gadget to see what frequency and temperature my chip was running it. These chips are all supposed to be able to hit around 100 degrees Celsius before throttling kicks in, but I would see the frequency drop down to ridiculously low numbers like 0.8GHz (on a supposedly 2.6 GHz machine) while under load and yet the temperature was less than 80 degrees. The fans however were going at max speed.

Took 20 minutes to open the underside panel of the Mac and blast compressed air outwards through the back and side vents. These vents are tiny and it doesn't take much dust over three years to block them. Hold the fans to prevent them from spinning and turning into unwanted generators. Ideally just get the Apple Store to do it for you if you have one nearby.

I tested the results before and after cleaning by running Prime95 for 5 minutes and then recording the CPU frequency. I also recorded how quickly the fans slowed down after Prime95 was stopped. If airflow is good, the fans should be able to quickly get rid of the lingering heat and then slow themselves down. And I got dramatically better results! On a heavy workload the frequency went up from 1.7GHz to 3.0GHz, and once it was finished it took less than a third of the time for the fans to return to effectively silent.

Graph of before/after frequency and fan speed attached.

TL;DR: If your Mac throttles even though the CPU temperature shows it should still have thermal room, it might be that your vents need a clean. If the vents are blocked other parts of the Mac heat up and the other temperature sensors will kick in and throttle the CPU to protect the overall system even if the CPU itself isn't in danger of overheating.

 

[Kissmyne]

Thank you for sharing this information, I'm sure many of us will find this of use.

 

[imorton]

Interesting...

I notice also that when I boot-up, my temps easily climb to 200'F and my CPU is at 100%

I am running a 24" external monitor, so just by running Mail, calendar, 10 tabs in Safari, and Activity Monitor etc.... my temps are usually around 150-160F

I wonder if blowing compressed air into the fan and surrounding area will help to drop temps...?


Hmmmm...

Thanks for the info, IAN.

 

[Samuelsan2001]

It's the same with all computers if you let them fill up with dust they get hotter quicker and can't cool properly causing throttling.

 

[maflynn]

I've done that with my computers on occasion, though I hadn't tried this with my MBP, mostly because how sealed it is. I don't think I'm that jazzed up right now to fully disassemble the computer to gain access to the vents and fan.

 

[makinao]

I wouldn't blow compressed air INTO a computer vent. It might just push the dust further into places where it can do more harm.

 

[klagermkii]

I notice also that when I boot-up, my temps easily climb to 200'F and my CPU is at 100%

I am running a 24" external monitor, so just by running Mail, calendar, 10 tabs in Safari, and Activity Monitor etc.... my temps are usually around 150-160F

I don't know if this would help there, that all sounds kind of normal. Those are roughly the numbers of my MacBook now! This is only helpful in the specific scenario where one is seeing the CPU maxed out in Activity Monitor, and yet things still feel really slow despite the CPU temperature remaining low (i.e. 180F, rather than being at the 210F the CPU is able to handle). I don't think the Mail/Calendar/Safari tabs will push it enough to show that problem.

I wonder if blowing compressed air into the fan and surrounding area will help to drop temps...?

I wouldn't blow compressed air INTO a computer vent. It might just push the dust further into places where it can do more harm.

Sorry I wasn't clear there! Don't blow the air into the vent from the outside that could compact the dust into something solid lodged in the fan. One's trying to get the dust out the machine not wedge it deeper.

I've done that with my computers on occasion, though I hadn't tried this with my MBP, mostly because how sealed it is. I don't think I'm that jazzed up right now to fully disassemble the computer to gain access to the vents and fan.

If you don't have this specific problem, don't do this just for fun. However I will say that this needs surprisingly little disassembly if you do have that 1.2mm Pentalobe screwdriver. Once the back panel comes off you don't need to remove anything else to do the cleaning. There's no black tape or whatever over the vents that have to be moved like in some previous MBPs. And compared to opening something like the 2007 MBP there are no horrible little clips that don't latch properly again resulting in it never being the same once you close it back up again. It's just straight forward screws.

Rather than doing it on a whim, this is mostly for people who are seeing kernel_task sometimes taking 150%+ CPU and need another suggestion worth considering.

 

[imorton]

Hi, thanks for the really helpful reply. It answers many of my questions.

Now I wanted to correct what I meant, I was going to take the screws off the bottom and BLOW OUT thru the fan etc.... Not blow INTO the unopened computer.

Now if I have a look at my MB Pro running Mail, Cal, Safari (10 tabs open), Activity Monitor, Console, Messages, the CPU its at 10-20% usage, and running 140-150F.

But when I also open Parallels Desktop and open up Win7, the CPU temps quickly climb and stay between 170-205F... Should it be this high without doing any really intensive work?

Thanks again for your helpful post... IAN