Old oil can get dirty. Dirty oil is not good for your car. The metal parts in your car slide against each other constantly and they do so at high speeds. If metal does not have clean oil to lubricate its movement it can generate a lot of heat. That heat can be very bad for your engine. The oil helps the metal parts to work together easily. Dirty oil can cause the parts of your engine to stall or to freeze up.
The more the oil is used to lubricate the movement of metal against metal the shorter the chains of the molecules become. The molecules break down and which brings the metal parts closer to rubbing together. In the long run, dirty oil can cause wear and tear on your engine.
When your oil is check, the mechanic will look at the color first. Clean oil is an amber color while dirty oil gets darker and darker until it is almost black. This is partially because it is getting dirty but it is also a reflection of the chemical breakdown of the oil.
If you want your car to last longer and run better, make sure you get your car’s oil checked on a regular basis. If the oil is dirty, have it changed. You will find that your car sounds better and that you have less problems over the long term.