Motor oil is an essential component for your vehicle’s engine. It helps ensure that all of the components run smoothly and require fewer repairs. However, not all motor oil is the same. If you put the wrong kind of oil in your vehicle, you can cause irreparable damage or at least a very expensive replacement. Before purchasing any oil for your vehicle, you need to know how to read the label.

The rating for your vehicle

Your vehicle must use a motor oil that has the correct service rating. This rating is given by the American Petroleum Institute. The oil must meet OEM (original equipment manufacturer) quality standards. You will see a symbol on the label of a motor oil showing this rating. The first thing you will pay attention to is the viscosity grade. The viscosity of a motor oil is how thick it is. The oil must be thick enough to adhere to the components as it passes by to provide adequate lubrication. At the same time, it must be thin enough to flow through the system.

Oil is given a viscosity grade based on how it operates in various temperatures. Oil must work in both heat and cold, and many modern oils have viscosity index improver additives included to ensure that it maintains the correct thickness for hot and cold temperatures.

The Society of Automotive Engineers has a classification system for grading oil viscosity. For multi-grade oils, which can be used in both winter and summer, two sets of numbers are usually present. The first number which is followed by a W for winter, may be a 0, 5, 15, 20, or 25. The second number is for the viscosity in hot temperatures, and it may be 20, 30, 40, 50 or 60. The most common oil grade seen is 5W-30. For the motor oil with the label 5W-30, the 5W means that the oil has a viscosity of 5 when the engine is cold, which is considered thin and means it will begin flowing even before the engine heats up. The second number 30 is the viscosity of the oil once the engine has heated up, and it isn’t too thin to provide proper lubrication for the components.

Service classifications

A two-letter code is listed on the motor oil label that tells you which types of vehicles the oil is designed for. It will begin with either an S for gasoline engines or a C for diesel engines. The second letter tells you which model years the oil is designed to work with. For the letter A, the oil meets requirements of vehicles that were developed before 1930. The classification of current vehicles is N, so that the two-letter code should read SN for new car owners.

This classification becomes very important for owners of classic vehicles, because the incorrect type of oil could harm an engine. Oils with the early designations have no additives to help protect your engine and may reduce performance or cause further harm. Current oils have numerous additives that are designed to protect various components in your engine. They include additives for oxidation control, to prevent corrosion, keep surfaces clean, minimize wear on the valve train, prevent rusting, and ensure seals don’t leak, among other functions.

Finding the information on the label

The viscosity grade is fairly easy to find on a motor oil label. It is often written in large numbers on the front of the carton. The service classification can be more difficult to find. It may or may not be listed on the front, but it is usually found in the information on the back.

The older oils may have unique descriptions attached to them, such as non-detergent or economy. Most states still allow for oils with early classifications to be sold and are often seen on the shelves with oils for current models.

Symptoms of using the wrong oil

If you use the wrong viscosity grade of vehicle oil, you won’t notice much difference as long as it is close in grade. However, the engine will wear down sooner and may provide lower performance.

If it is the service classification that is wrong, you could reduce your vehicle’s performance and cause serious damage. Emissions will increase and your engine could break down from many causes because of the lack of protective additives in the oil. It is important to have a trusted, professional mechanic change the oil in your vehicle and ensure that the correct oil is used. If the wrong grade or classification of oil is used and damage results, you may have voided your warranty.

This article originally appeared on YourMechanic.com as How to Read a Motor Oil Label and was authored by Joyce Morse.


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