Fan cap is now 3085 instead of 2700 on iMac

[Annv]

I recently had an issue with fans ramping up due to high load on iMac. Unable to locate the reason, I run a Catalina 10.15.5 Combo updater, and this seems to fix the issue.

But in MacsFanControl the max fan speed is now 3085, not 2700 as before. Is it a recent change?

 

[Annv]

Update: The issue of high fan speed has not been solved. The fan ramps up much easier/earlier than before.

I had to apply a custom profile in MacsFanControl to make the fan quiet again.

 

[TiggrToo]

Update: The issue of high fan speed has not been solved. The fan ramps up much easier/earlier than before.

I had to apply a custom profile in MacsFanControl to make the fan quiet again.

Are they ramping up due to temperature? If so, then artificially slowing then down isn't perhaps the safest thing to do.

The only reason I use the app is to engage cooling at lower temperatures. I'd rather fans and a longer life as opposed to the opposite myself.

 

[Annv]

Are they ramping up due to temperature? If so, then artificially slowing then down isn't perhaps the safest thing to do.

The only reason I use the app is to engage cooling at lower temperatures. I'd rather fans and a longer life as opposed to the opposite myself.

I believe the fan is ramping up due to temperature (switched to Auto to be safe). But I have an impression that it does so at lower temperatures than before. I have CPU PECI sensor data and fan speed always displayed in the menubar. The fan used to remain at 1200 rpm with 62 and even 69 degrees Celsius, but now it's already at 1250 rpm, sometimes at 1300 or 1400 or higher.

It might be because it's quite hot these days. But it could be because a recent update has changed something. I've never seen a cap of 3085 rpm before. And I heard this 3100 rpm jet sound when a Windows VM was updating.

I wouldn't mind a higher fan speed, but the iMac becomes audible at anything over 1200 rpm, and it has quite an unpleasant and distracting frequency, right in front of my head.

 

[chrfr]

It might be because it's quite hot these days.

An increase in ambient temperature will absolutely have a noticeable effect on computer cooling.

 

[tyc0746]

The other thing to consider is if Apple are seeing temp related hardware faults, so have recalibrated the temp tolerances to see if it helps?

 

[Annv]

Here is a screenshot of the sensors and rpm levels. Temperature is not high, and yet the fan has already slightly sped up. I'm sure it didn't happen before.

This might be the case, I believe:

The other thing to consider is if Apple are seeing temp related hardware faults, so have recalibrated the temp tolerances to see if it helps?

 

[Annv]

I couldn't bear the noise and switched to custom fan profile with TG Pro app at my own risk. Surprisingly, the minimum speed is now 1150 rpm instead of 1200 rpm — and that's where it stays most of the time. CPU PECI rarely goes over 69 degrees Celsius, which is a normal temperature for this machine (I always have CPU PECI sensor/fan speed info in the menubar).

iMac is a bit warm, but not warmer than usually.

I believe the iMac is designed to stay quiet under most scenarios. Its fan noise is unbearable at any speed over 1300 rpm.

I really wonder why nobody noticed this change in temp curve.

 

[mj_]

This is a very interesting observation indeed. I wonder whether it's because of your Core i7 CPU, because I am also running macOS 10.15.5 Catalina on a 27" 2017 iMac but mine has the the base model Core i5 instead of the upgraded Core i7, and my fan curve and temp curves did definitely not change at all:

The default minimum is still 1200, and the maximum is still 2700. However, I have been running my fan at the lowest possible setting of ~940 rpm for a very long time now (using the SMC hack that I found here on these forums a while back) because it's just so much quieter and nicer. I rarely ever see my CPU going above 55°C during normal workload and maybe 70°C tops when I really push it. I have 65°C set as the temperature where fan speed will start to increase from and 90°C as maximum temperature.

 

[Annv]

This is a very interesting observation indeed. I wonder whether it's because of your Core i7 CPU, because I am also running macOS 10.15.5 Catalina on a 27" 2017 iMac but mine has the the base model Core i5 instead of the upgraded Core i7, and my fan curve and temp curves did definitely not change at all:

View attachment 924677

The default minimum is still 1200, and the maximum is still 2700. However, I have been running my fan at the lowest possible setting of ~940 rpm for a very long time now (using the SMC hack that I found here on these forums a while back) because it's just so much quieter and nicer. I rarely ever see my CPU going above 55°C during normal workload and maybe 70°C tops when I really push it. I have 65°C set as the temperature where fan speed will start to increase from and 90°C as maximum temperature.

Thank you for sharing this info.

My CPU temperature is at 55-59°C when starting the computer and is usually at 60-69°C during the day. And the ambient sensor shows 42°C now. I've never seen such low temperature (or anything even close to them) as on your screenshot. I guess my maxed out components might be too hot for this iMac cooling system. I should have chosen some average configuration.

Among other things, I also notice now that the screen saver (like Drift) makes the fan go crazy (at or above 2000 rpm), which did not happen before.

It started at some specific moment several day ago (maybe macOS upgrade, maybe some other program). Not gradually increasing, as if it were because of accumulated dust. And the ambient temperature is not that high again. So really strange, especially those new min/max levels.

 

[chrfr]

Thank you for sharing this info.

My CPU temperature is at 55-59°C when starting the computer and is usually at 60-69°C during the day. And the ambient sensor shows 42°C now.

What's the actual ambient temperature in the space where your computer is located?

 

[Annv]

What's the actual ambient temperature in the space where your computer is located?

It's 22°C now, but it was 28°C today and over 30°C for the last few days.

It might also be relevant that I use iMac as max brightness and further decrease it with Gamma Control app, to reduce eyestrain. But I've been doing it for a long time already.

 

[chrfr]

It's 22°C now, but it was 28°C today and over 30°C for the last few days.

This is why your computer is running hot. Using the computer in 28-30ºC temps means that the computer is already quite warm before it's even turned on. Using maximum brightness will also increase the thermal load. There's absolutely nothing abnormal about your computer's operation.

 

[Annv]

It might have been some glitch.

I do not even know how it got fixed. I deleted a couple of apps that I installed recently but didn't actually use (Cocktail, MailMate). I also switched off Gamma Control, moved the brightness slider back and forth, switched on Gamma Control, switched off TG Pro and switched on Macs Fan Control. I might have done some other things that I cannot recall... Maybe macOS finished doing some indexing or else.

It's now back to its normal behavior, the temperatures inside the computer are much lower, and the case is not warm. Now I'm not even sure what the CPU temp levels were before all that started (mid 50-ies or mid 60-ies).

 

[mj_]

Do (or did) you have smcFanControl installed by any chance?

 

[Annv]

Do (or did) you have smcFanControl installed by any chance?

Yes, I've checked now and it is installed, but not running. Is it known for adverse effects?

 

[mj_]

Not necessarily, but it could in theory. smcFanControl comes with a command line utility called smc that you can use to read from and write to your computers SMC directly. This is how I lowered my FanMin value down from 1,200 to 940rpm. Maybe some other application used it to decrease/increase the FanMin (F0Mn) and FanMax (F0Mx) settings on your iMac. However, those should get reset anytime you reboot your computer, and you have to manually apply those settings every time.

I do also not believe that ambient temperature had anything to do with what you experienced. First of all increased ambient temperatures might be the reason for increased fan activity and higher temperatures in general but it won't mess with the FanMax and FanMin settings as those are like I said programmed into your iMac's volatile SMC memory. Second, I keep my thermostat at 78F (26°C) but my office does get a bit warmer in those brutal Texas summer afternoons due to the cathedral ceiling and lack of insulation, and my iMac has never reacted to those hot days compared to the cold ones in winter. My 15" MacBook Pro was definitely hotter and louder in summer but not the iMac, so I don't believe it had anything to do with your increased fan activity.

 

[Annv]

Not necessarily, but it could in theory. smcFanControl comes with a command line utility called smc that you can use to read from and write to your computers SMC directly. This is how I lowered my FanMin value down from 1,200 to 940rpm. Maybe some other application used it to decrease/increase the FanMin (F0Mn) and FanMax (F0Mx) settings on your iMac. However, those should get reset anytime you reboot your computer, and you have to manually apply those settings every time.

I do also not believe that ambient temperature had anything to do with what you experienced. First of all increased ambient temperatures might be the reason for increased fan activity and higher temperatures in general but it won't mess with the FanMax and FanMin settings as those are like I said programmed into your iMac's volatile SMC memory. Second, I keep my thermostat at 78F (26°C) but my office does get a bit warmer in those brutal Texas summer afternoons due to the cathedral ceiling and lack of insulation, and my iMac has never reacted to those hot days compared to the cold ones in winter. My 15" MacBook Pro was definitely hotter and louder in summer but not the iMac, so I don't believe it had anything to do with your increased fan activity.

Thank you, I will need to investigate on the FanMin (F0Mn) and FanMax (F0Mx) settings to try to understand what's happened. And you are right about ambient temperature: it's still hot here, but the fan does not speed up. It also ignores short term temperature spikes and stays at 1200 rpm — exactly like it was before.

 

[Annv]

I still do not know why the maximum fan speed was sometimes higher than 2700 rpm, but the overheating and the fan ramping up were caused by the dust for sure.

I have vacuum-cleaned the air inlet grid on the bottom and the air outlet on the back of the iMac. The dust layer was so dense on the bottom, that I had to scratch it with a toothpick before vacuuming it. As a result, the temperature dropped by 5 to 10˚C.

Before that, it seemed that the fan didn't manage to exhaust all the heat, so the temperature and the fan speed were gradually increasing over time. The case was getting quite warm, even hot in one area.

Now I can feel the difference!

It's just the first day after I've cleaned out the dust, but the fan hasn't ramped up a single time, even under heavy load like starting a virtual machine (UPD: after some more testing I can see that it actually ramps up sometimes, but for very short periods of time, and the heat is removed really quickly). The case is overall cool and sometimes slightly warm in the area where the hot components are located. The air flow is enough to remove all the heat.

I'll be repeating this cleaning once a few months, not to let it happen again