I am getting erratic behavior when I adjust the upper thread tension knob on my sewing machine. For example, no matter how slowly I adjust it, it's either too loose or too tight. Or during sewing the tension would suddenly change from slightly loose to way too high despite me not touching the knob.
I am wondering if it happens because I don't oil the tension discs. If I am supposed to, doesn't that mean that the thread will become greasy during sewing? And won't thread just immediately wipe the oil off of discs?
I couldn't find an answer to my question on the Internet. Everyone just says that the machine needs to be oiled, but nobody says if the thread tension discs should be oiled too.
My sewing machine is pretty old. I have lost the instruction manual, and I couldn't find a copy on the Internet.