What does the 'w' in motor oil specifications mean?
4 Answers
The 'w' in motor oil specifications stands for 'winter', indicating that the oil can be used normally during winter if it contains 'w' in its specification. Motor oil, also known as engine lubricating oil, serves to lubricate and reduce friction in the engine, assist in cooling, seal against leaks, prevent rust and corrosion, and provide shock absorption. Motor oil consists of two parts: base oil and additives. The base oil is the main component of lubricating oil, determining its basic properties, while additives compensate for and improve the shortcomings of the base oil, imparting certain new properties, making them an important component of lubricating oil.
The 'W' stands for 'winter', indicating the oil's low-temperature fluidity in its viscosity rating. For example, in the 5W-30 grade, the '5W' means the oil can remain fluid at -30°C—the lower this number, the better the low-temperature performance. The '30' represents the high-temperature viscosity; a higher number means stronger high-temperature protection. Folks in Northeast China should opt for oils starting with '0W', like 0W-20, which flows smoothly even at -35°C, ensuring smooth cold starts without engine dry grinding. Those in the south can use 5W, but remember—don’t just focus on the numbers before and after the hyphen; always follow the maintenance manual. Using excessively high-viscosity oil can actually increase fuel consumption.
After ten years of repairing cars, I've found that many car owners don't understand the secrets behind motor oil viscosity ratings. The number before the W indicates the oil's cold-weather performance - for example, 0W oil can flow at -35°C while 5W withstands -30°C. This number directly affects engine protection during cold starts. Once during a customer inspection, I found his car using 15W oil. After sitting overnight at -25°C in Harbin, the oil was thick as honey in the morning - the oil pump couldn't even circulate it. Switching to 0W-30 solved the problem immediately. Nowadays, new cars mostly use low-viscosity oils like 20-weight grades, which improve fuel efficiency and provide faster lubrication to precision components.
The mysterious codes on engine oil containers are actually quite simple. Take 5W-40 as an example: the W acts like a separator, with the left number indicating cold weather performance and the right number representing high-temperature viscosity. When choosing oil, first look at the number before W - this determines cold-start capability. Northern regions should use 0W or 5W, while 10W suffices for southern areas. The high-temperature number must match your manual - German cars often require 40 viscosity to protect turbos, while newer Japanese models typically use 20 viscosity for fuel efficiency. Never blindly believe 'higher viscosity means better protection' - using the wrong viscosity actually accelerates engine wear.
