What is a good thermal margin?

gustavo.mazuco · Nov 3, 2017

Hello, everyone!

I have an FX CPU and tried to stress test it to see if it was stable and within good temperatures. I saw that the temperature readings were wrong and asked around.
People said that the temp reading on FX CPUs really doesn't work well and recommended me to use AMD Overdrive and look for the thermal margin temperature instead, so i downloaded it and ran another stress test to see what readings i would get and i got about 58-60C on idle and 36C while stress testing on prime95 with small FFTs (i think that's the name).
From what i read, thermal margin represents the distance from the current temperature to the maximum temperature but i don't know what is my CPU's maximum temperature, so i'm not sure about the results. Can anyone help? is a thermal margin of 36C during prime95 a good temperature?

Oh, and my CPU is an FX-4300 with a Hyper T4.

Thanks in advance!

mrmez · Nov 3, 2017

TBO I've never heard of 'thermal margin', but given those chips run hot, and you haven't listed your cooler (which usually means something stock or low end), I'd say that doesn't sound right.

If you assume a temp limit of around 90c, with a 'thermal margin' 36c, leaves the actual temp at 54c, which is VERY low for a cpu at full load. Even for a custom water loop and a thermally efficient cpu (which the FX series are definitely not), you won't be getting those numbers.

Again, not 100% on AMD cpu's, but that generation ran VERY hot, so safe to assume that at full load it's nearing it's thermal limits.

gustavo.mazuco · Nov 3, 2017

mrmez :

I did mention my cooler. I said it is a Hyper T4. Apparently it is impossible to read the right temperatures on FX CPUs with normal programs like HWMonitor or Speedfan and people say that the only way to get an accurate reading is by the thermal margin reading on AMD Overdrive, or at least that's what i read. All the other programs say my CPU temp is around 9C at idle and 20C at full load, which is absolutely wrong.

mrmez · Nov 3, 2017

Gotcha, missed that.
Yeah, 95w tdp is a pretty big ask for that cooler. Depending on ambient temp etc, I'd GUESS between 10c and -5c thermal margin, meaning you could likely experience thermal throttling on a stress test, but probably be fine for gaming.
At this stage probably not worth upgrading the cooler, but you can be pretty sure if you push the cpu it's going to get close to it's limits.

Rogue Leader · Nov 3, 2017

gustavo.mazuco :

This is a useful article on this subject

http://www.tomshardware.com/faq/id-2122665/understanding-temperature-amd-cpus-apus.html

The TLDR is the idle numbers are useless and incorrect, however your load number of 36 is correct and that is very good. Bad is if it gets down around 10 or 5.

Your system is stable with very good temperatures. If you have a good motherboard you can probably overclock it a bit.

gustavo.mazuco · Nov 3, 2017

Rogue Leader :

gustavo.mazuco :

This is a useful article on this subject

http://www.tomshardware.com/faq/id-2122665/understanding-temperature-amd-cpus-apus.html

The TLDR is the idle numbers are useless and incorrect, however your load number of 36 is correct and that is very good. Bad is if it gets down around 10 or 5.

Your system is stable with very good temperatures. If you have a good motherboard you can probably overclock it a bit.

Really? So 36C is a good margin, then? That's a relief! Thanks so much for the help!

mrmez · Nov 3, 2017

https://www.techpowerup.com/reviews/beQuiet/Shadow_Rock_2/6.html

Well.. on max load an 84w CPU will hit 78c with a better version of the Hyper T4 (Hyper 212 EVO), so I have a hard time believing a 95w CPU with a worse cooler is running a massive 24c cooler.

Again, I'm assuming ~90c max for OPs cpu. So a 36c thermal margin = 54c under full load.
36c IS a great margin. I just find it hard to believe that number.

According to the link, the corsair H100 water cooler manages 71c.
I have this cooler, and playing pCars2 yesterday (which is not full cpu load), with an 88w cpu, it was holding steady at ~68c at min fan speed. So their results seem a good match to mine.

Make of it what you will, but there is definitely evidence to suggest these numbers don't add up, possibly due to:
-36c reported thermal margin is incorrect
-CPU max temp is much higher than 90c (over 100c)
-Your room is actually a fridge
-Prime95 test isn't actually applying max load

Rogue Leader · Nov 4, 2017

mrmez :

You're looking at this all wrong. First off the max temp on an FX-4300 is 70c. Some FX processors are as low as 65c.

That said how the temperature is measured is different on AMD FX processors as well, so "70c" on an AMD processor is higher on an Intel Processor because of where the temperature is measured from.

At stock clocks with proper cooling, its very conceivable that his processor is running at approximately "34c" under load in Prime95.

You have to be careful answering these types of questions for different processors not all work the same. AMD Processors up to but not including Ryzen handle temperatures much differently, and its virtually impossible to get a true idle temp out of them.

Karadjgne · Nov 4, 2017

TjMax on all FX cpus is 62°C. However, FX cpus don't have 'on-core' thermal strips the way Intel cpu's do, so getting exact temps is kinda impossible. So what overdrive does is read the temp by subtracting the number from TjMax. The closer to Zero you get, the closer to 62°C you are getting.
Realtemp, Coretemp, speccy and most other temp readers are written generally or specifically for Intel cpu's, so when trying to read an FX cpu, the result is about as accurate as a blind man at the gun range. What you'll get instead from those that attempt accuracy is an algorithm derived temp, not an actual temp, and based on the @100°C standard Intel uses. So in those readings, you'll see temps of 70ish°C or higher, but actual temps are closer to mid 50's out of the possibility of 62°C. Because of the algorithm, you'll get idle temps of 18°C, even though that's impossible in a 22°C ambient by mechanical means. Which makes idle temps basically useless except in relation to norms. (if stock idle is 18 and OC idle is 30,there's an issue).

Reading FX temps and trying for any kind of simple, one step temps accuracy like Intel has, is basically an exercise in futility. Just run Overdrive and stay higher than the 'teens' and you are good.

gustavo.mazuco · Nov 4, 2017

Karadjgne :

Yes, exactly. Other programs read the temperature as something very low, which doesn't make sense. However, you said that the tjmax should be 62C, right? From what i gathered, thermal margin is the distance between current temperature and the maximum temperature. Since you said that the maximum is 62C and the margin showed on overdrive was 36, then would that be 62-36=26? Then is my temperature during prime95 26C? That doesn't sound right. Maybe it doesn't work like that or i got something wrong?

Karadjgne · Nov 4, 2017

No, you got it right. Much depends on how you ran p95. Running small fft runs the cpu at 100% load, balanced fft runs the cpu at less but uses more stress on the ram, and large fft is easiest on the cpu, using a lot of ram. This makes large fft harder on the system overall, but easier on the cpu.

Also, you have to remember that you have a cpu cooler doin it's job. This is going to change the temps drastically. With an AMD stock cooler (they truly are pathetic for those generations) your margin would be much closer to 0°, so you'd be looking at temps closer to mid 50s or higher under p95.

To put it in perspective, my i5-3570k with a little 120mm aio gets 57°C under p95 26.6 small fft at stock values (3.4GHz), with a 4.3GHz OC itd a flat 70°. That's 43-30°C thermal margin. If you are seeing a 36° thermal margin, then you are pretty much good.

Rogue Leader · Nov 4, 2017

THe only correction to above is that the max on this CPU is 70.5 not 62. Not all FX have the same max temp.

http://products.amd.com/es-xl/search/CPU/AMD-FX-Series/AMD-FX-4-Core-Black-Edition/FX-4300/94

Karadjgne · Nov 4, 2017

TjMax for all the FX cpus is 62°C. However, socket temps can vary from 70-72°C and is often referred to as max temp, even by Amd, as getting accurate TjMax readings is next to impossible, but you can get somewhat accurate socket temps as there are thermocouplings in the socket itself.

http://www.overclock.net/t/931241/interesting-information-from-amd-about-1090t

Rogue Leader · Nov 4, 2017

Karadjgne :

In there he is referring to the prior Phenom cpus though, not FX, and he never says where overdrive reads from, but I always assumed it to be the socket temp sensor (don't remember where I read that)

Karadjgne · Nov 4, 2017

Yep. AMD seems to have made this whole temp thing about as ambiguous as it could possibly get.

And while the cpu itself in that is a phenom, not fx as such, they are both am3+ and work the same, even if different actual architecture. What I was trying to point out is that while the cores temp TjMax is in fact 62°C, many, including amd themselves, use the socket temp of 70°C as max as that's readily able to be read accurately, having actual sensors on the mobo underneath the cpu, not so much a speculated temp based on algorithmic guessing. What kinda sucks is there's no actual standard like Intel uses, any temp reader is able to read the temp as posted at that particular address. With Amd it's a guessing game with no particular point of reference.

TjMax (core temp) = 62°C
Tcase (cpu temp) =70-73°C
Thermal shut down = 90°C
Silicon starts melting at 97°C +

That's everything I can find from every source. And no, I couldn't find where Overdrive actually reads from either,but sources have hinted at it reading originally from TjMax then in comparison or collaboration with Tcase and AMD's funky algorithms 'guessing' at a temp that owners can understand and make use of. Pretty much the only thing that is understandable in the relationship to 0. Stay out of the teens if possible, if in single digits get a better cooler or adjust usage. If you see negative numbers, bail.

gustavo.mazuco · Nov 4, 2017

Rogue Leader :

Karadjgne :

But if the max temperature of my CPU is 62C then my core temperature in overdrive would be 26C as i've said before. Could it really be that low with prime95? I think 70C would make more sense. In fact, Core Temp (the program) shows my tjmax as 90C, but i'm not sure if i can trust it anyway.

Rogue Leader · Nov 4, 2017

CoreTemp (the program) is useless.

The point he is trying to make, and I agree with, is forget about what the temp is itself, and just know that what you are reading from Overdrive is showing its running more than safely. You have nothing to worry about

gustavo.mazuco · Nov 4, 2017

Rogue Leader :

Okay, then. Thanks, guys!

Karadjgne · Nov 4, 2017

You are thinking Intel. In comparison to Intel temps. For the FX, thermal shutdown is 90°C, beyond that you are starting to damage the cpu heavily, get beyond 97°C and you are actively melting the silicon.

It's like this. Silicon is an insulator, it doesn't pass either electricity or heat well at all in comparison to metal. Cores themselves never see actual 100% usage, there's always breaks in string code as strings are shuffled around the threads. So the cores heat/cool almost instantly, but things like the IHS (cpu lid) stay at an almost constant hot, so see higher overall temps. So while the cores might be averaging 26°C, the cpu itself could be seeing 55°C, and that'll be Tcase (cpu temp) which is what most readers will use as that temp comes from a sensor underneath the cpu, inside the socket, and has an actual address that's accessible. A mailman can guess how many ppl live in a house based on the size, but knows for a fact Mr Jones lives there cuz that's the name on the mailbox.

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