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Car Oil Differences: Viscosity, Grade, Type, and Usage

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Dan has been an auto mechanic, truck driver, engineer, and many other things.

Become familiar with engine oil differences.

Become familiar with engine oil differences.

What Is Engine Oil and Why Does My Car Need It?

Oil is the substance that lubricates the internal moving components of your vehicle's engine. There are many different types of oils on the market suitable for car engines, but there are some basics that you should know before deciding which to purchase.


This is simply how readily the oil flows. A higher-viscosity oil will withstand more heat than a lower-viscosity oil. However, at colder temperatures, it can actually become so thick that your starter cannot turn over the engine—and worse yet, it won't flow to all the moving parts it should.

A viscosity that is too low won't maintain a lubricating film on engine parts, allowing them to make metal-to-metal contact.

Either extreme is very bad!

Single-Grade vs. Multi-Grade

Single-grade engine oils (such as SAE 30) used to be the standard for engines operating at high temperatures (such as air-cooled engines). Since the advent of the American Petroleum Institute (API) rating system, the multi-grade oils that proliferate on shelves nowadays are suitable for nearly all applications.

An older gentleman told me that his '30ish Ford won't build oil pressure with multi-grade oil—but then again, I'd be surprised if his '30ish Ford builds oil pressure at all.

(Fun fact: SAE stands for "Society of Automotive Engineers," the association that established a code system for grading oils based on their viscosity.)

Selecting Your Grade

Which oil you should choose will mostly depend on what you're driving. If your car is not an antique or air-cooled, the safest bet is to use a multi-grade oil. The first number on a multi-grade oil indicates the "cold" viscosity of the lubricant, and the second number the "hot" viscosity.

For example, an SAE 10W-40 motor oil would have a viscosity rating of 10 at 0-degrees Fahrenheit (the W indicates "winter") and a 40 rating at its maximum recommended temperature (not engine operating temperature—ambient air temperature).

The following chart is a good place to start. Determine the temperatures you'll be driving in and select an oil accordingly.

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Different oil grades perform better in different temperatures.

Different oil grades perform better in different temperatures.

Other Factors for Choosing the Right Motor Oil

Everyone has different scenarios in their personal driving situations, so making a decision on oil for your engine isn't a "one size fits all." Keep these factors in mind when you're making your decision.

Driving Conditions

Consider your driving habits and the condition of your car. If you drive hard—keeping the engine near redline for extended periods, or you do a lot of high RPM "freeway" driving—then you may want to select a higher-viscosity oil for your car. Also, if your engine is high mileage, a high-viscosity oil will keep it a little quieter and may not slip through the rings to be burned (blue smoke).

Age of Car

If your car is newer, you will most likely want a lower-viscosity oil. This is true of most newer high-performance cars also—they too have tighter bearing tolerances and recommend a low-viscosity oil (it doesn't rob as much power from the engine).

Winter Weather

Overall, if you expect very cold weather ahead, definitely choose an oil with a lower "cold" viscosity. If you live in a warmer region, a higher winter rating (the W rating) will help keep your cam and valves from clattering when you first start your car.

Keep in mind your personal driving considerations when selecting an oil for your vehicle.

Keep in mind your personal driving considerations when selecting an oil for your vehicle.

Types of Motor Oil

Drivers should also be aware that there are different types of motor oil, and some are better than others for your particular vehicle.

  • Conventional: The most commonly used oil for simple-design, low-to-average mileage cars is also the most affordable.
  • Full synthetic: This is recommended for peak performance vehicles requiring high levels of lubrication. Note that it's more expensive than other oils.
  • Synthetic blend: This special formula is a hybrid of conventional and synthetic oils.
  • High mileage: This specially designed oil was formulated for older cars with more than 75,000 miles.
A car mechanic, dealer, or the manufacturer website will usually have good information about what oil you should use for your vehicle.

A car mechanic, dealer, or the manufacturer website will usually have good information about what oil you should use for your vehicle.

Check With the Experts

If you're still not sure about the most suitable oil for your vehicle, local weather conditions, or your own personal driving habits, it's always best to check with an expert to get the right information for your situation.

  • Owner's manual: This is a great place to start.
  • Trusted mechanic: Your local trusted mechanic has worked on countless vehicles and probably knows the best oil for your car.
  • Dealership: The dealer's service department knows more about your specific car than anyone.
  • Manufacturer: It should be easy to find all the things you need to know about your vehicle on the manufacturer's website.

This article is accurate and true to the best of the author’s knowledge. Content is for informational or entertainment purposes only and does not substitute for personal counsel or professional advice in business, financial, legal, or technical matters.

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