Why do I have to change my motor oil?

There are several reasons why it is important to make a regular change of motor oil. The main purposes of oil are to lubricate, cool and clean. The older the oil gets the less effective it is at these jobs and it becomes more likely that the engine will suffer from low oil pressure and use more oil because of it. Remember that low oil pressure, or lack of oil, is extremely damaging to your engine. If the oil pressure gauge shows that the pressure is too low, or if the oil warning light illuminates on the dashboard you should take immediate action.

All this used to lubricate the moving parts inside the engine. Without oil moving parts such as the pistons inside the cylinder is turned bearings on the camshaft would rub against each other as they worked. This rubbing would cause wearing tear leading to damage and, because of the extreme heat, even friction welding of components. In other words the engine would become useless. Oil provides a cushion for the moving parts to glide over there for preventing contact and prolonging usable life. However, as oil pages it becomes dirtier. Microscopic fragments of metal and other debris become suspended in the oil as it gets older. To some extent this is a good thing because it removes dirt from the engine but once the oil is saturated the particles inside it acts like a scrubbing brush when the oil is squeezed together by moving parts. This is one reason why oil needs to be changed, to get rid of detritus before it begins to damage the engine.

Motor oil also contains additives to change its mechanical properties. This includes properties such as its viscosity, which is a measure of the thickness of oil. When oil is cold it is thicker, or more viscous. This inhibits its ability to circulate around the engine, which it needs to do to lubricate and cool. When oil is hot it gets thinner, again this reduces its ability to lubricate. additives are used to reduce the effects of hot and cold temperatures on the oil and to keep the viscosity more consistent. Additives are also used to clean the engine, this prevents a buildup of black sludge inside the engine, which if left untreated makes it harder to maintain oil pressure. Over time these additives get used up and this is another reason why oil needs to be replaced.

Oil also cools the engine. By coating every internal surface heat is transferred to the oil from the metals. If black sludge is preventing the oil from coming into contact with the metal and is reducing the oil pressure then it is harder for the oil to cool the engine with sufficient speed. Because of all these reasons it is important to change your motor oil on a regular basis.

Often taken from granted, understanding your engine's oil system, is a critical part of looking after your car. Read more about it at the Oil Pressure Gauge Guide site and at my other hubs.