Understanding motor oil

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Changing your car’s oil is a simple task, but there are many varieties of oil to choose from. Do you know which oil is right for your car? Learn about oil weights and types, to determine what’s best for your vehicle.

Why a Regular Oil Change?

The regular oil change is a car owner’s most important routine maintenance chore. Your car’s engine needs oil to lubricate high-speed moving parts, and the oil gets dirty over time. That dirt builds up and creates friction which can damage moving parts if the dirty oil stays in the system long enough.

The Right Oil: Weight

Which type of oil is right for your car? Check in your car manual; you can also find it printed on the oil cap under the hood. Depending on your vehicle’s make and model, you may see one of the following printed on the cap:

  • 5W-20
  • 5W-30
  • 10W-40
  • 15W-40

These numbers refer to the "weight" or thickness of the oil. Motor oil gets thicker when it’s cold and thinner when it heats up. 5W-30 oil performs better when it’s cold — it flows more easily when you first start the vehicle. Your mechanic may recommend 5W-20 or 5W-30 oil for very cold climates, even if the manual recommends 10W-30 or 10W-40. Unless you’re taking the advice of a trusted mechanic, always use the oil type recommended on your oil cap or in the car manual.

The Right Oil: Type

In addition to the oil’s weight, there are different types of oil, which include:

  • All-synthetic
  • Synthetic blends
  • High-mileage
  • Premium conventional

All-Synthetic Oil

All-synthetic oils perform better than ordinary petroleum-based oil, but they are more expensive. They're recommended for luxury vehicles and other high-value cars and trucks. There are car owners who prefer using fully synthetic oil in their car or truck, even if it's not a luxury vehicle.

In many cases, there's nothing wrong with using synthetic oil in a standard vehicle (costs aside), but get the advice of a trained mechanic before making the switch. In some cases, a vehicle may have a specific need for either a blended synthetic or a standard, petroleum-based oil. Be sure to check your owner's manual.

Synthetic Blends

Synthetic blends are a combination of petroleum-based oil and the synthesized version. Blends perform well in SUVs and other large vehicles. This oil type is also less expensive than full synthetics.

High-Mileage Oil

High-mileage oil is made especially for cars with 75,000 miles or more on the odometer. Using high-mileage oil in these older vehicles helps you get more life out of the engine.

Premium Conventional Oil

Premium conventional oil is standard for brand-new cars and should be changed every 4,000 miles, every four months or when your oil-change indicator light comes on — whichever happens first.

Used with permission. © 2015 Walmart. All Rights Reserved. See full legal.

Used with permission. © 2014 Walmart. All Rights Reserved. See full legal.


Important Walmart Disclaimer: Proper service and repair procedures are vital to the safe, reliable operation of all motor vehicles as well as the personal safety of those performing the repairs and those riding in the motor vehicles. Standard safety procedures and precautions (including use of safety goggles and other safety equipment, proper tools and equipment) should be followed at all times to limit the possibility of personal injury or improper service which could damage the vehicle or compromise its safety.  Personal injury could result from the failure to take adequate safety precautions when repairing or maintaining your vehicle.  Although this material has been prepared with the intent to provide reliable information, no warranty or representation (express or implied), including the warranties of merchantability and fitness for a particular purpose, is made as to its accuracy or completeness. Neither is any liability assumed for loss or damage of any kind resulting from reliance on this material and Wal-Mart shall not be liable for any loss or damage of any kind resulting from reliance on this material.  Users employ the information contained in this material at their own risk.  This material is provided only as a helpful guide and does not replace the information and instructions contained in the motor vehicle's owner's manual and product manufacturer's recommendations.  Users are cautioned to consult the motor vehicle's owner's manual and product manufacturer's recommendations for additional information and instructions.   Failure to follow the motor vehicle's owner's manual and the product manufacturer's recommendations could result in damage to your vehicle or personal injury.  Additionally, users should be aware of the applicable laws of their local jurisdiction.


Any product information is provided by the supplier or manufacturer of the product and should not be construed as advice. Wal-Mart does not sponsor, recommend or endorse any third party, product, service or information provided on this site.


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