You have just asked one of those questions which returns quite often wives tales .... dust retention etc. is one of them !!
Brushless motors are usually maintenance free as they rarely fail before the model does. Unlike older Brushed motors that often need brushes or replacement.
BUT Brushless motors are working in a lot of environments that were previously unheard of for Brushed motors - due to their power outputs etc.
The Phantom motors are mounted making it difficult to lubricate if you want to ... because the motor wires are short to the ESC. They were never mounted with a view to maintenance.
This does not mean they are to be forgotten though IF deemed time to sort.
There is a mis-conception going round that DJI motors are sealed ... that is wrong. They are SHIELDED motors. This means that the motors are constructed to restrict dust / debris entering the bearings but does not mean they are sealed for life. There is also mis-conception that they are lubricated for life and that oiling will somehow destroy this. I can only say that those who keep posting these mi-conceptions have most likely never had a DJI motor out or dismantled.
Is it necessary to oil ? usually no.
Can they be oiled ? Yes
Is this detrimental to the motor ? Absolutely not detrimental.
What oil to use ? The best oil to use is Sewing Machine Oil or as we call it in the trade ... Light Cycle Oil (LCO). If you do not have that then a reasonable substitute is 3in1 Bicycle oil.
When to lubricate ? If you have noted a change in sound of the motor due to dry bearing or after dust etc.
Once you lubricate is it necessary to repeat often ? No. Only if condition repeats that prompted initial lubricating.
Now on to how .....
You need to have the correct driver to undo the four motor screws. A marker board pen that can be wiped off after. A couple of cocktail sticks or very small thin screwdriver. Bottle of LCO or 3in1. Tissues. Bottle of Blue grade Plastic safe Thread lock.
Mark arm you are going to work.
Unscrew motor screws and allow motor to move.
Have model upside down so motor wants to drop out ... it won't as the wires are short.
Angle the motor so you can apply a small drop of oil with the toothpick point at base of the shaft ...
While still inverted - spin the motor by hand ... apply another small drop ... spin again ... this lets the oil being thin wick in.
Dab excess away with tissue.
Motor back in place and resecure using tiny amount of threadlock on motor screws.
Move to next one. Note the mark you made on arm for first one reminds you where you started !!
All done. Power up and a quick powered spin up of the motors - just starting them is enough ... stop and put her away till you fly.
What you will note in the 'How to' ... is that you only oil from the rear UNDERSIDE of the motor. You cannot do much about the front bearing. The rear bearing is face down into the bottom of the arm and is also enclosed by the plastic around it.
I have over 60 Brushless motors in models incl. DJI and when I think needed - I lubricate any of them. I have had some squealing in use after dusty summer etc. - the above sorts and quiet again. I have motors I have oiled for many years continue to provide excellent service long after first oiling. The only DJI motor I have that does not work - was one that was submerged in the dirty river water. All others have had an odd oiling now and again .... they fly absolutely sweet as new ...
There is a big difference between a squeal from dusty summer ... to the screech of metal on metal ....Nigal says : I have had some squealing in use after dusty summer !
"Once that teeny tiny itty bitty small bearing has sent out a LOUD SQUEAL" !
That Only means that that ball bearing has encountered metal to metal...and after that its on its way to destruction as its Once smooth surface is Not smooth No more !..and in the future is a candidate for sudden failure !
As a tear falls out of both eyes and your drone falls to the ground from 399 feet UP.
If a wheel bearing on your car starts to squeal Would You oil it and go about your way (NO) period !
Please never use WD40 on any model gear ... in fact I can tell you that when I raced cars in my early 20's .. I had an arrangement with local auto service that I would do the electrics repairs in return for use of their lifts etc. So many cars had ignition trouble in those days from people who thought spraying WD40 liberally over distributors and points etc. was good idea .... it is awful stuff.Hi can they not be lubricated with a bit of WD40 or would that not be suitable! does it have to be sawing machine oil ? Cheers
Do the motors have to be oiled on Phantom 3 Standard and how if needed
Twaddle ...bunkum ....No!! DJI Phantom 4 and Phantom 3 Quad motors DO NOT require oil and if you believe they do, then I have a bridge in Brooklyn that I'd like to sell you.
I would highly recommend that you go to the DJI Forum (https://forum.dji.com) where they will tell you NOT to apply oil to DJI Phantom 4 or Phantom 3 motors.
DJI has also been asked this question numerous times and they too DO NOT recommend the practice of oiling the motors on the Phantom 4 or the Phantom 3 quads.
DJI Quad motors require NO OIL WHATSOEVER but please, don't take my word for it. Simply ask DJI themselves if oiling the motors will affect your warranty.