[One (M9) General] Valerio-M8:
As you may know, our beloved smartphone suffers from some overheating problem, due to the powerful Snapdragon 810 that use.

Its cores are the real "cores" of the problem: Qualcomm has adopted pure ARM reference design instead their revised versions, that creates more trouble than it should;

No custom kernel or other things really solve the problem and the results are bad performances in heavy load scenario (multitasking or gaming) and more heat than usual.

To be honest, I never had any particular problems with my M9, but wanted to try something that I also done on my old M7: disassemble the phone and apply a serious-level thermal grease to make sure to put processor die in contact with the metal body!

Well, let's start!

Here's what I am faced: a carefully disassembled One M9 (iFixit exhaustively explains how to do that) and, at my discretion, the best thermal paste on the market, the Artic MX-4.

Now i gently opened the metal coverage of components and ... There is our processor!

At this point, i have to remove the old (and inefficient) thermal pad applied by the factory.

-In the photo i've already partially removed it.

The instant after the compound application.

Pressure will definitely flatten it; it's also a large surplus but in that way i'm sure that it will cover the entire surface of the processor and also the surroundings. (no problem, it does not conduct electricity)

After closing the coverage, I applied a dose of thermal paste also on it, to bring together the processor with the outside of the smartphone, according to the scheme below.

Now we're ready to clo...HEY! wait, wait, wait, is a missing screw what I just saw?

YES! and also explains my perception of the slightly lower volume from the bottom speaker!

Fortunately, M7 screw are compatible... screwed and fixed!

... is not an oversight that I would expect from this flagship device...

...as I was saying, I reassembled the smartphone.

No one will notice anything, like new!

And now, you will expect results ... here they are!

I made this improvement more than one month ago, at the time I done many many tests, i also take screenshots, but they're totally useless at the moment, because what you should know is the following;

In addition to the significant drop in temperature outside of the phone, as I noticed with my old M7, I have seen an unexpected increase in battery life of 10% of the daily average, really not bad!

And the temperature of the processor? It's now under control! Even under full load, the temperature increases gradually and slowly, without peaks and never exceed 45 degrees on the cores, even after several minutes of use.

In normal use, temperature is a few degrees above the ambient one.

To ensure that my system works well I did a little test... I launched a benchmark app (viewing onscreen temp) and after a few minutes I put an ice cube on the back of the phone, just above the processor position: I assisted to an insane temperature drop, from 45 to 7 degrees Celsius within 8-10 seconds!

What to say, I am pleased of the change I made to my M9, now the problem is not completely resolved but it is dammed.

Remember, I shared with you my experience for information, I do not assume liability for damage to your smartphone!