Motor oils are rated based on their viscosity, or flow-resistance, and their performance at extreme temperatures. An ideal motor oil is one that can brace against a region’s hottest temperatures while still being able to withstand a flow through the weather at its coldest.

The Society of Automotive Engineers (SAE) has formulated a numerical code system for grading motor oils in accordance with their viscosity-related characteristics. Since the viscosity of oil fluctuates with temperature, multi-grade oils were developed to provide protection across a wide range of temperatures and climatic conditions, hence the come-up of label names like 5W-30.

5W-30 oil is a light-duty multi-grade motor oil which is can be used in lightweight petrol diesel and gasoline engines (multi-grade oils are motor oils with ascending viscosity grade). The ‘w’ in the name of the oil stands for ‘winter’, and the number ‘5’ preceding it represents the lower limit of the viscosity grade, whereas the number ‘30’ succeeding it represents the upper limit of the same. The lower limit applies for low temperature conditions (hence the abbreviation for ‘winter’), such as when the engine is turned off or is running in frigid environments. The upper limit applies for high temperature conditions, such as when the engine is turned on. 5W-30 oil is suited to a wide range of temperatures, and therefore it is the most commonly-used oils on the automobile accessory market.

5W-30 oils are favorably different from other oils in a variety of considerable ways, deeming “suitable for use” in most vehicles. They have a winter viscosity grade of five, making them less thick at very low temperatures than oils like 10W-30, for instance. Similarly, their hot viscosity grade is 30, making them less thick in high temperatures than, say, 5W-50 oils. 5W-30 oils can function effectively in temperatures ranging vastly from -30°C to 35°C. The viscosity range allows it to lubricate, seal and protect the engine’s internal components in a range of various external climatic conditions. Another additional advantage of this feature is the lack of strain it causes on the oil pump, as well as the provision of a better fuel economy.

5W-30 oil is a highly-preferable multi-grade motor oil for lightweight locomotives (similar to 10W-40 oil for heavy-duty vehicles), and is widely-used because it is fluid enough to flow at extremely low temperatures, and glutinous enough to perform efficiently and satisfactorily at high temperatures as well. However, some setbacks to the pros of this oil are the region of residence (for example, Finland, subjected to frigid temperatures, would normally deem 0W/5W-30 oils as broadly suitable, whereas Nigeria, located in close proximity to the equator, would normally require 5W/10W/15W-40 or even 20W-50 oil), the vehicle purpose and requirements (i.e. lightweight or heavy-duty), and the vehicle’s condition with specific respect to age and maintenance. Other factors kept in disregard, 5W-30 is certainly one of the most widely-merited oils for a majority of the automobiles in common use, and may certainly be used in the general maintenance of one’s average, everyday-running car.