If your electric motor is fried you will often know by the smell of burnt wire and burnt windings and burnt insulation as well as smoke coming from the electric motor.
Also seeing visible burn marks or charring on the electrical windings in the motor and a burnt smell coming from the motor are signs that the electric motor is fried.
A fried electric motor is severely damaged and is often not worth repairing unless it's a very expensive and large electric motor.
Electric motors can be rewound and rebuilt but smaller and cheaper electric motors that are fried are not often worth rebuilding as the cost to rebuild and rewind the electric motor can cost more than just purchasing a new electric motor.
The causes of an electric motor to catch fire are over voltage, overloading the electric motor, worn bearings, poor ventilation, dust buildup, moisture contamination, electrical issues, incorrect wiring, too much oil or grease in the bearings.
Also overworking the electric motor and running it for too long of a time without breaks can lead to the electric motor overheating and cause a potential fire or failure of the electric motor.
Rotor overload, moisture damage, insulation failure and bearing failure can all cause electric motors to fail and catch fire or even running the electric motor at too high of RPM and too high of voltage.
You can over oil an electric motor and over oiling an electric motor could actually cause more wear and tear on the bearings and too much oil in the electric motor could seep out away from the bearings and get into the electric motor windings which can cause the motor to fail and smoke.
When oiling an electric motor you put between 2 to 4 drops of oil into the electric motor for each bearing, depending on the size of the electric motor.
Generally you can just put the oil into the electric motor a drop or two at a time until the oil reaches the top of the oil port.
Avoid over oiling the electric motor though as it can cause damage.
Electric motors require oil if the electric motor has oil ports which are located on each end of the motor housing where the motor shaft exits the motor.
Some electric motors have sealed bearings and don't require any oil and if there's no oil ports or grease ports the electric motor does not need any oil or grease.
But if the electric motor does have oil ports or grease ports they need oil or grease to keep the bearings lubricated.
The kind of oil that you use in a small electric motor is often 3 in 1 motor oil or SAE 20 motor oil.
The best oil for electric motors including small electric motors is 3 in 1 motor oil or SAE 20 motor oil.
3 in 1 motor oil or 3 in 1 oil in general is best for electric motors for lubrication.
3 in 1 motor oil is the best for electric motor bearing lubrication.
SAE 20 motor oil can also work in electric motors for lubrication.
WD-40 is OK for electric motors when cleaning and freeing up any stuck components although WD-40 shouldn't be used as a lubricant for the bearings as WD-40 is not an actual lubricant but is instead mainly a cleaner and penetrating solvent.
3 in 1 motor oil is different than the regular 3 in 1 oil.
Some larger electric motors may require grease or a thicker oil depending on the size of the electric motor although most household sized electric motors can use 3 in 1 motor oil or SAE 20 motor oil.
10W 20 motor oil or other light oils can also work for small electric motors.
And for electric motors that need grease, the grease consistency preferred for electric motors is normally NLGI 2 or 3, with a base oil viscosity of 100-150 cSt @ 40°C or 104 F.