How to Read a Motor Oil Label

Motor oil is the lifeblood of any combustion engine. Although the oil products used today have evolved from crudely refined conventional oils to laboratory created synthetic oils, using the correct engine oil is an essential part of vehicle maintenance. 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, or too much or too little, you can cause irreparable damage or at least a very expensive replacement.

Before purchasing any oil for your vehicle, it is important that you understand how to read the label correctly.

Understanding the Type of Oil Required for your Vehicle

Before you purchase any oil, the first step is to know what type of oil your car, truck or SUV uses. In general, there are three types of motor oil:

*Full Synthetic Oil *Conventional Oil *Synthetic/Conventional Blend Oil

Inside the owner's manual of any vehicle is a section that talks about the right engine oil that must be used for your vehicle. This will break down the type of oil into different sections including:

*The type of engine oil (Synthetic, Blend, or Conventional) *The viscosity rating of the motor oil, which will be written in a format similar to this: 5W30

This rating is given by the American Petroleum Institute or Society of Automotive Engineers. You will see a symbol on the label of motor oil showing this rating. The viscosity of motor oil is how thick or thin 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 easily flow through the system. There will be two numbers, a low number and high number. The low number indicates how thin the oil is rated to be, while the larger number is the thicker rating of the oil. Engine temperature typically determines the thickness of the oil.

For the motor oil with the label 5W30, the 5W means that the oil has a viscosity of 5 when the engine is cold, which is considered thin and means it will flow even before the engine heats up. The second number (30) is the viscosity of the oil once the engine has heated up.

Understanding the 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 owners of relatively new, gasoline powered cars.

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 if used improperly.

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. Mixing synthetic motor oil with conventional oil and vice-versa can cause the engine to develop lubrication problems, damage internal engine seals and gaskets and lead to overheating problems.

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 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.

In most cases, having a professional mechanic complete your engine oil and filter changes will reduce the potential of having the wrong motor oil added to your vehicle. It is always a good idea to check your engine oil once per month, to ensure your oil level is at the recommended level. YourMechanic always uses the highest quality Castrol oil in every oil change.


The statements expressed above are only for informational purposes and should be independently verified. Please see our terms of service for more details

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