iM 4,1-14,4 Running hot: Core i5 - late 2009 - 27"

[exploradorgt]

Hi everyone, is this normal? The top left of the computer gets a bit hot. It's a Core i5 750.

• Average original CPU temperature on idle: 70 Celsius
• After cleaning the CPU and replacing the thermal compound (Arctic MX-4): 65 Celsius
• After cleaning again and replacing the thermal compound using something generic: 55 Celsius
• Now using Macs Fan Control (2000 RPM for CPU): 42 Celsius, I think it's quite good, but the top left still gets too hot in my opinion

For context: I've checked the tempts using software and with my own hands while moving away the screen, it's confirmed, it's the CPU, only the top left is being affected. And yes, I made sure the vents and fans are clean and working fine.

I took my time searching the web before posting, and found A LOT of users complaining about thermal issue with this specific model, most with the graphics card (GPU) but this is not my case, the card is just fine (read above). Found one specific story explaining my exact situation: CPU temp being reported within range, but the top left is still hot. Most responses and testimonials suggest "it's normal, and to be expected".

• Perhaps it's just me? because I'm used to modern computers not running this hot?

I'm currently using the Windows power plan options to set a maximum of CPU usage (yes, I'm running Windows 10), and this is what's keeping the temps low, but it's nothing fancy, full cpu usage on the profile gets the temp to 49. Wait, Windows VS Mac? I've found people discussing OS differences but this is not the case.

Funny thing (RAM), during my searches on the web, found the detailed story of a guy reporting trying many diff things, until finding out THE RAM was causing the overheating (his case), found 3 similar stories to this one. His thread ends with him exploring the RAM modules. I'll try this myself a bit later (8G ram). BTW, there are threads on the web reporting increase of temperature after increasing their RAM.

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Let me explain the background.

Bought this computer second hand with a GPU issue (originally the HD 4850 gpu), but anyway the CPU got really hot while using MacOS High Sierra, I think it's safe to consider the GPU problem as a separate situation. Baked it, worked, bu the CPU still got hot (remember, top left of the computer). This went on until I got a GPU replacement and it's working perfectly fine, the graphics card stays really COOL. But the CPU still gets hot. After loosing the boot screen I due to the GPU change, I just didn't want to bother with drivers, injecting or flashing, so I removed MacOS and placed Windows instead using a SSD (DVD caddy), all the temperature sensors are in place working fine. The machine literally flies, it's really fast. In short, the CPU getting hot it's a thing since before experiencing graphics card issues, I explain this just to keep the situations separated.

I own other computers (way more modern), they run pretty damn cool. My daily driver it's a 24" desktop, but for some tasks I appreciate the 27 inch screen, I don't mind using this Mac-Win randomly and NOT as my daily driver, I just don't want to burn energy as heat.

* Fun fact: many years ago at the office we had Apple Macintosh 8100 (and other models) PowerPC's with Apple displays, these things would get so hot we often placed our sandwiches there for a while before the lunch time ha ha.

 

[MultiFinder17]

I've always found that the 2009-2011 iMacs, especially the 27" ones, make fine little space heaters. I have a 2010 i7 27" that I used for a year as my main computer in my classroom and my students would often comment when they came near my desk how hot my computer was. I now use it in my office off the side of my classroom and it quite effectively heats up the small room when it's on for a while, and the back top is hot to the touch. It's been repasted, Macs Fan Control, all that good stuff and it's still a big honking' furnace that sucks down power like nobody's business. Welcome to the old 27" iMac club my friend, hope you live somewhere cold

 

[jmilan0302]

It's the display, my mid 2010 27" is literally too hot to touch in the top left. 100W idle usage. Cools down pretty quickly with the display off. The inverter has no ventilation at all and the power supply gets the heat of the 95W TDP CPU to cool it. Maybe the HDD fan could be redirected to cool the PSU instead.

 

[exploradorgt]

I've always found that the 2009-2011 iMacs, especially the 27" ones, make fine little space heaters.

[...]

It's been repasted, Macs Fan Control, all that good stuff and it's still a big honking' furnace that sucks down power like nobody's business. Welcome to the old 27" iMac club my friend, hope you live somewhere cold

Thanks, that's quite relieving, it's the model then.

How interesting, my previous daily driver laptop (Asus) had a Core i5 and never got nearly even half as hot, nor on idle or in full use, the cooling and ventilation flow was really efficient. My mac is now holding the 35 Celsius steady, it's even lower than yesterday, I see it's fine then.

It's the display, my mid 2010 27" is literally too hot to touch in the top left. 100W idle usage. Cools down pretty quickly with the display off. The inverter has no ventilation at all and the power supply gets the heat of the 95W TDP CPU to cool it. Maybe the HDD fan could be redirected to cool the PSU instead.

Wow I didn't expect this, quite surprising. I kept the mac without the screen screws to check the temperatures -by hand- for a while, the GPU stays cool (to the touch), but the CPU got really hot along with the screen, I thought the CPU and it's heatsink transferred the heat to the screen, but now I understand the screen heats on it's own. I'll explore using the mac with remote desktop (full screen off) to see what happens.

But yes, it makes sense, the cooling flow is quite terrible by design.

 

[Procrastinus]

A basic law of thermodynamics is that the outlet cooling vent should be the same or larger than the inlet.
So, to enlarge the thin restricted top vent of my 11,1, I drilled two 8mm holes at either end of the top narrow ventilation slot and used an angle grinder to connect the holes, a file finished off any rough edges and silver auto paint matched the existing finish. I should mention, remove glass and screen first and tape up the inside top grill to keep swarf out of the machine. Sounds rough, but with care one can achieve an excellent finish. I was inspired by this! MacFan did the rest.

 

[Nguyen Duc Hieu]

My iMac 2009 is hot at its whole top, not just a specific corner.
Looking from the front, the top left is supposed to be hotter, as the hot air ventilated through the CPU heatsink and the PSU heatsink.
The top right has only hot air from the GPU.
But the whole thing is terribly hot if you keep the LCD panel at max brightness.
In my case, I have a Quadro M4000m oveclocked, and LCD panel at max brightness. So no wonder.

 

[exploradorgt]

I drilled two 8mm holes at either end of the top narrow ventilation slot and used an angle grinder to connect the holes

Cool, I was thinking about this too, but didn't dare (yet). I was having multiple issues with the GPU, until I finally replaced it, right now I'll wait a bit before making any drastic modifications (one gets tired of tearing everything down over and over). But yes, I see how this works.

I was inspired by this! MacFan did the rest.

Nice. Sadly it seems it was just a painkiller pill for the moment. Someone asked the author about a follow up video, this is the response:

it's dead. I would probably have had to make a hole right behind the video board and installed a fan.​

The video was posted on 2013, the response is from 5 years ago (2023 - 5 = 2018), so it seems the computer only lasted 5 years after the mod (no details on what happened).

My iMac 2009 is hot at its whole top, not just a specific corner.
Looking from the front, the top left is supposed to be hotter, as the hot air ventilated through the CPU heatsing and the PSU heatsink.
The top right has only hot air from the GPU.
But the whole thing is terribly hot if you keep the LCD panel at max brightness.
In my case, I have a Quadro M4000m oveclocked, and LCD panel at max brightness. So no wonder.

Also relieving, now I know it's confirmed as a common issue.

I have the Quadro 1000m, no changes made at all, it works pretty well, fresher than the original HD 4850. I'm running Windows, just... sometimes the brightness control doesn't work, usually does after a restart, but it's something.

 

[ToniCH]

I've had 2 x late 2009 27" iMacs and 2 x mid 2011 27" iMacs. They all run very hot on top, mostly on the left side. Right now with iMac 27" 2011 i7 3.4GHz the CPU core 1 temp is, while browsing this forum and maybe some others at the same time, +46-48°C. At this temp with Macs Fan Control and based on sensors the fans run very quietly. CPU fan runs at +100 rpm over minimum. I can barely hear this when the room is totally silent.

I think the iMac chassis works as a heat sink and that is normal.

 

[Procrastinus]

I think the iMac chassis works as a heat sink and that is normal.

Never quite believed that thoery personally - it seems a very inefficient way to cool electronics especially with such a large vent available underneath.

I think the follow up to this was that he did not change the GPU card to a non-standard one. I have fitted a K1100M and temps are never above 50C

 

[exploradorgt]

It's the display, my mid 2010 27" is literally too hot to touch in the top left. 100W idle usage. Cools down pretty quickly with the display off. The inverter has no ventilation at all and the power supply gets the heat of the 95W TDP CPU to cool it. Maybe the HDD fan could be redirected to cool the PSU instead.

Yes, that could work. I'm still surprised on how hot the LCD gets. Had an old 32" TV around a few years back and got hot, but neeeeever this hot.

However, redirecting air or adding fans would only move air. The components might stay cooler, but doesn't mean the heat is not being produced and energy is being wasted. I tried today using the computer via remote desktop (naturally with the screen fully off) and the imac remained cool.

Two ideas come to mind:

1. It would be interesting to intervene the LCD LEDS connectors (the 12 pins + cables), putting a few resistors to reduce the current sent to the LCD, this would mean less brightness but also less heat (considering an efficient selection of resistors).
2. Creating a completely independent inverter circuit would do the a better job, instead of reducing the current via resistors it should produce less current out of the box, if I had an extra board and connector I would try it myself, but I don't. So far I don't want to cut the present cables.

*Now it makes sense why the board controllers (to turn the LCD into some standalone screen) have reduced brightness (it's been reported on multiple threads and forums). The screen should stay cooler while also showing less brightness.

** Perhaps all of this relates to Apple refusing to make more 27" computers.

 

[ToniCH]

Never quite believed that thoery personally - it seems a very inefficient way to cool electronics especially with such a large vent available underneath.

Well, fresh air is sucked from underneath and fans blow upwards so heat ends up in top of the case naturally, hot air exhaust is maybe 1cm below case top. They could have made the exit vents bigger but I guess they also need to control how much dust enters the case. I think they try to create overpressure inside the case to minimize dust inhalation? Ie. intake is bigger than exhaust. That doesn't work too well though as the iMacs I've opened are usually quite dusty inside. Maybe noise level has something to do with the design too? Compromise, like they often are.

Took a quick measurements from my temps right now:
- cpu temp 48°C
- top left case temp 42°C
- top right case temp 39°C

The case temp is lower than I expected, feels hot to touch.

 

[exploradorgt]

I would love to get another 2009 - 27" iMac to play with it and mod the LCD backlight placing a custom inverter (to avoid messing the one I just fixed).

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Specifically about the brightness (LCD backlight) The way I see it, the backlight stays too bright no matter what, yes, I can modify the brightness and contrast, but I see the brightness control is modified via the color leds on top, not because the backlight is adjusted or dimmed, like on my other computers.​

​

Keep in mind this context: I replaced my GPU recently, and I don't remember this detail when I was just running High Sierra. The thing is, I do have full control over brightness and contrast, but I can see the cursor stays bright. This means the backlight stays the same, it's just the color-leds-layer on top doing the adjustment. On other computers when you modify the brightness, the whole LCD gets a PWM signal adjusting the overall electric signal. I'm not sure if what I'm seeing applies to High Sierra too, or if it's disguised by also painting the cursor with a diff color. Anyway... in my case I can clearly see the LCD is not being dimmed (even that I'm getting the visual result I want via brightness-contrast).​

 

[Nguyen Duc Hieu]

I would love to get another 2009 - 27" iMac to play with it and mod the LCD backlight placing a custom inverter (to avoid messing the one I just fixed).

- - - - -

Specifically about the brightness (LCD backlight) The way I see it, the backlight stays too bright no matter what, yes, I can modify the brightness and contrast, but I see the brightness control is modified via the color leds on top, not because the backlight is adjusted or dimmed, like on my other computers.​

​

Keep in mind this context: I replaced my GPU recently, and I don't remember this detail when I was just running High Sierra. The thing is, I do have full control over brightness and contrast, but I can see the cursor stays bright. This means the backlight stays the same, it's just the color-leds-layer on top doing the adjustment. On other computers when you modify the brightness, the whole LCD gets a PWM signal adjusting the overall electric signal. I'm not sure if what I'm seeing applies to High Sierra too, or if it's disguised by also painting the cursor with a diff color. Anyway... in my case I can clearly see the LCD is not being dimmed (even that I'm getting the visual result I want via brightness-contrast).​

For Quadro Q1000m, I think there is some lines in the inf files or Regedit you can change to get the backlight control back to Windows.
Hardward wise, there is a PWM module you can insert between the logicboard and the LCD backlight control board to adjust LCD panel brightness. Need an Oscilloscope also to verify the correct frequency.

 

[DCBassman]

Interresting to find this thread. I'm new to Macs, and I'm typing this on a 27" late 2009 Core 2 Duo machine. It got hot just as you said. When it was opened for SSD install, I hoovered out a ton of dust. Didn't help, so MacsFans it is. Unlike @ToniCH I prefer fixed values for the fan speeds, having tried both ways. So, ODD = 1500rpm, HDD = 2000, CPU = 1800. Silent essentially, although I might be able to hear it if I closed all the windows! Only faintly warmer in the top LH corner, everywhere else cool.
Yesterday I got a 21.5" 2011 i5 iMac, and that's installing Monterey as I type. It's warm, but cooler than it was when OCLP was doing its thing preparing everything. I'll do the same experiments with MAcsFans once it's up and running and see if it prefers constant speeds, or if the sensor-based system works better on that model.
I am expecting the room to be less cold this winter!

 

[ToniCH]

I prefer fixed values for the fan speeds

Fixed values have one potential problem: if for what ever reason components start to heat up more than the fixed value can handle nothing is done to reduce the heating event. When its sensor based the fans will ramp up when needed. And note that you can adjust the fan speeds by adjusting the trigger temperatures. So, you can make the fans to run faster than normal by increasing the lower end value but you are not limiting the top rpm it can use if/when necessary. And you can make the fan speed go to max earlier by reducing the top value.

 

[DCBassman]

Fixed values have one potential problem: if for what ever reason components start to heat up more than the fixed value can handle nothing is done to reduce the heating event. When its sensor based the fans will ramp up when needed. And note that you can adjust the fan speeds by adjusting the trigger temperatures. So, you can make the fans to run faster than normal by increasing the lower end value but you are not limiting the top rpm it can use if/when necessary. And you can make the fan speed go to max earlier by reducing the top value.

I'll be playing with it some more, definitely. As and when I get the two iMacs upgraded as I want (memory for the i5, cpu and memory and a new optical drive for the C2D), I'll be switching for a while away from Windows, to see if I can actually live with macOS as a daily driver. If so, fine, if not, they'll become Linux machines, and I'll have to find a whole new way to control the fans! Linux is not yet that wonderful in terms of iMacs in this context, as far as I can see.

 

[exploradorgt]

Interresting to find this thread. I'm new to Macs, and I'm typing this on a 27" late 2009 Core 2 Duo machine. It got hot just as you said. When it was opened for SSD install, I hoovered out a ton of dust. Didn't help, so MacsFans it is. Unlike @ToniCH I prefer fixed values for the fan speeds, having tried both ways. So, ODD = 2300rpm, HDD = 2300, CPU = 1900. Silent essentially, although I might be able to hear it if I closed all the windows! Only faintly warmer in the top LH corner, everywhere else cool.
Yesterday I got a 21.5" 2011 i5 iMac, and that's installing Monterey as I type. It's warm, but cooler than it was when OCLP was doing its thing preparing everything. I'll do the same experiments with MAcsFans once it's up and running and see if it prefers constant speeds, or if the sensor-based system works better on that model.
I am expecting the room to be less cold this winter!

I definitely thought about what @ToniCH said above, it's sure something to consider. Yet, in my case I've been testing the machine over and over, and even getting really hot on "automatic" (Macs fan control), the system never kicks the speed above such levels (Mine: 1900 CPU / 2300 HDD / 2300 GPU). After reading around, I found people explaining it doesn't take let's say 70 Celsius for the system to kick in and raise the speeds, it does so only at higher temperatures... that's not something I expected, I guess the whole system tries to keep the speed of the CPU and GPU until the last moment.

To make some sense out of this... at least in Windows, it's configured for active cooling by default, meaning the system will try to keep the speed while increasing the fans RPM to cool everything down. I did the opposite: I configured everything for passive response, meaning throttling... my system will lower the CPU speed to cool everything down.

It's fair to say I've been testing this with both-eyes on the temperature sensors (Fan speeds on fixed values: 1900 CPU / 2300 HDD / 2300 GPU), and yes, the temperatures stay on healthy ranges. CPU stays between 35-45 Celsius, highest? 50 Celsius. The LCD proximity reports 61 maximum, it really stays around 54 Celsius. And the GPU heatsink and GPU card stay at 43 Celsius maximum. I think those numbers are really great!

* Keep in mind: this 2009 - 27" iMac is not my daily driver!!!! and not meant to become the main computer at my office. I have more modern and way more efficient computers, my daily driver works insanely fresh (24" screen, even on heavy tasks, yes, it's AMD, not Intel, way more efficient for heat and power usage). My 27" is for editorial work due to the bigger screen, that's Indesign / Canva / Word, no design, just editorial.

** Updated: current fan speed values.

• The fan noise is far (higher) compared to what I'm getting from my daily driver computer (24" HP AMD)
• As it is, the noise is similar to my previous Core i5 Asus laptop at high CPU usage
• And... it is fairly comparable to the normal noise of a desktop (tower) computer at normal CPU usage

 

[DCBassman]

Currently, @exploradorgt and @ToniCH , the 27" C2D is running sensor-based with nothing above 47C. The 21.5 i5 machine runs much warmer, but I'm certain that it needs a really good clean and the thermal paste doing, and I'm sure that will help.

 

[MultiFinder17]

I should grab the temps from my 2010 27" i7 at school tomorrow - it has had its HDD swapped for an SSD and it's running Ventura, so Macs Fan Control all the way.

 

[ToniCH]

Currently, @exploradorgt and @ToniCH , the 27" C2D is running sensor-based with nothing above 47C. The 21.5 i5 machine runs much warmer, but I'm certain that it needs a really good clean and the thermal paste doing, and I'm sure that will help.

From something somebody said in another thread I suddenly remembered: in 2009 27" C2D the power supply is located in left top corner just above the cpu heatsink. I think its PSU that makes the top left of the case so hot rather than the CPU. Same fan cools both the cpu and the psu.

According to Macs Fans Control my (iMac 27" 2011) cpu is now 47° and the PSU is 59°. So it might be the same thing with the 2009 models?

EDIT: I see Nguyen Duc Hieu already addressed this earlier. Well, anyway...

 

[DCBassman]

Neither of the iMacs I have are helped by being near a window, and we're having something of a heatwave...

 

[exploradorgt]

Neither of the iMacs I have are helped by being near a window, and we're having something of a heatwave...

I made an accessory 2 days ago. Been testing it, and it works quite well.

Used a metal plate about 1mm thick, easily bent using a press and a hammer to get the shape shown above, then I glued it to the fan using transparent epoxy. The fan is an ordinary 12v unit (0.28A, low energy consumption), but instead of driving it at 12v, I'm using just the 5v from the USB port (or a powerbank). The way I bent the metal allows about 1 and a half inch in between. The nice thing about this is, you can put it there, move it to the sides, and remove it as needed. It's very low level noise.

The results are quite good. Keep in mind:

1. The heat is produced inside the case
2. The heat is dissipated by the heatsinks and expelled via the top of the case
3. The dissipation of the computer is very limited by-design, so, the case heats up, and then the case sort-of behaves like a heatsink, but not really. The heat should dissipate via direct contact, but it's not a great idea anyway because the whole thing would heat up in a diff way and would affect the other components. Here, instead of a solid, the heat is being transferred to the case mostly by AIR, so, the capacity of heat dissipation of the aluminium is being affected by the transference in between (air) that's why (among other factors) the dissipation is quite bad. Air behaves mostly as an insulator (air has terrible heat conduction).
4. Cooling the case would help... should help... it helps... It's not like you will see -5 Celsius right away on your sensors, this is just a way to transfer heat from the case FASTER to the surroundings, and if you have enough ventilation you see the results.

What I'm seeing: cooler temperatures on the case, the top left remains quite cool, and this does affect the temperature of the LCD (in positive). Those who can sense the heat of the screen in their eyes would notice a difference, that's what happens to me, at some point I could feel the heat in my eyes, this is helping a lot 🙃. You can compare this to using the computer on your backyard with natural wind. Sure... as explained on #1, the heat is produced inside and still will be produced, this just helps for confort and stops the accumulation of heat.

It is the same effect as laptop coolers, the heat will still be produced, these things just help to move it away faster.

The way I see it, drilling holes in circle behind the PSU and adding a small flat fan (yes, placed INSIDE, that works way better) and it would do a better job, but at this moment it's not something I want to do.

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I also tried adding a "vertical fan" right below the screen, perfectly aligned to the air intake. I played with 5v to 12v and noticed the fresh air coming out of the case vent with the computer off, then tried using the computer and it worked, but to get a minimal effect the noise was too high, and the heat was still accumulating at the top left of the case, so... no thanks. As others have explained here and there, it's not exactly the air intake, it's the outlet, too limited.

 

[ToniCH]

I am sure every little thing helps. My solution is to not worry about the heat of the case so much but heat of myself. I let the Macs Fans Control worry about the computers. I have a 10cm 5V USB fan aimed at me, cooling me down when I sit in front of my iMac. I often have other computers running too so it gets hotter than I feel comfortable, especially during summer. But, even during winter I rarely need to turn heating on in this room. And I live in the Nordics. 😂

 

[DCBassman]

If the grille under the stand of an iMac is meant to vent heat, then maybe some means of positioning a smaller fan over it to make it an active vent might help. Again, a 12v fan run at 5v would be quiet, but might have a reasonable effect?

 

[ToniCH]

If the grille under the stand of an iMac is meant to vent heat, then maybe some means of positioning a smaller fan over it to make it an active vent might help. Again, a 12v fan run at 5v would be quiet, but might have a reasonable effect?

What? No, I might misunderstand you but.... heat goes up and fan blow direction is up. So, intake is under the case and exhaust is the thin wide slot in the upper backside of the case. Here I am using my english skills and thinking vent means letting the heat out of the case (?).