oil tends to turn black if the oil hasn't been changed in over 6000 miles. or you have lots of soft carbons built up in the motor
how to resolve
1. change your oil at 3000 miles unless its synthetic (6000 miles)
2. get a motor vac. its like 80$ it removes all the gunk outa of the injectors. run marvel mystery oil or lucas to prevent soft carbon build up
sources : personal experence my dad is a ASE master Tech
Common causes, blower motor resistor, blower motor, wiring or controls
Starch.
Rusting
Mold
what caused the motors to turn faster
Poor circulation. You should see a doctor immediately!
Gravitation.
Ck the heater fan motor resistor .
No, go see a doctor immediately!
Brake dust!
Bugs are wiping their asses on them
There is likely an internal short circuit in the fan motor.