Synthetic Versus Conventional: Which Motor Oil is Best?

Which motor oil is the best?

As the lubricant for the moving parts of your engine, motor oil is widely considered to be the most important fluid you can use. It prevents excessive engine wear and tear, which makes it vital to keep your car running. So when the time comes to get under the hood do an oil change, you can bet you’ll want to know whether to buy synthetic or conventional oil.

What You Need to Know
There are three main types of oil – conventional, synthetic and synthetic blend. Conventional oil is organic—it’s essentially refined crude oil that’s been pumped up from the ground. Synthetic oil is manufactured molecule by molecule, and because of that, synthetics have fewer imperfections in their chemical buildup than conventional does.

In general, synthetic oil outperforms conventional oil on all counts:

  • Synthetic oil works better in extreme temperatures from below freezing to above 100 degrees Fahrenheit. Conventional oil is highly reactive to temperatures.
  • Because synthetics have superior lubrication (they’re more slippery), they give you better fuel economy, performance, and even a longer engine life.
  • And best of all, synthetics don’t have to be changed as often. But make sure you meet warranty service mileage intervals regardless.

The only downside to synthetic oil is it costs more than the regular stuff. But before you choose pennies over performance, crunch the numbers—with longer oil change intervals, the price difference might be a wash.
Synthetic blends, or “semi-synthetics”, add synthetic additives to conventional oil and can be a nice compromise between the two. They’re less expensive but provide some of the performance enhancement you get from a synthetic.

These three types of motor oil will work fine in your vehicle as long as they meet current American Petroleum Institute (API) certification and don’t go against the manufacturer’s recommendations. The only type of engine you should never use synthetic oil in is a rotary. Rotary engines have unique seals that are engineered for use with conventional oil only.

Pro Tip: Check that you’re not voiding your warranty by using the wrong oil. Many newer vehicles require that you use synthetic oil and some synthetics aren’t approved for certain diesel engines.

The Final Say

When buying oil for your car, the best thing you can do is to follow your manufacturer’s recommendations. So, check that owner’s manual! When you consider that the wrong oil can cause an engine to fail, it pays to take their suggestions seriously. If you have the option to choose between synthetic and conventional and still aren’t sure which to pick, consult a pro—they’ll know what to do.

Synthetic motor oil: an overview

Advance Auto PartsSynthetic types of motor oil were first available for cars in the early 1970s. AMSOIL was the first with a product, in 1972, with Mobil Oil Company following suit three years later. By the early 1990s, most major oil companies had synthetic options in their product lines and now it seems as though there are new brands every year.

As the name suggests, synthetic oil is a lubricant that is artificially made from chemicals, rather than directly from crude oil, although some synthetics start with crude oil as its base. There are also synthetic blends that contain conventional oil along with no more than 30% man-made fluids.

Advantages and disadvantages of synthetic oils

Synthetic oils were originally created for use in jet planes with high-temperature engines. So, not surprisingly, this man-made oil flows better than conventional oil in extreme heat. It also operates better in extremely cold temperatures. These oils:


  • have lower rates of evaporation, which means that less oil is consumed
  • have less sludge buildup
  • can help with fuel economy
  • cause less wear on the engine and therefore help with engine longevity

Overall, a synthetic choice holds up better over a longer period of time; this is why some manufacturers state that users can go longer between oil changes. As a caution, pollutants build up in the engine with conventional OR synthetic motor oil and so it’s important to follow recommendations given in your car manual.

Synthetic motor oils are more expensive, typically twice as much as conventional oil, because of the added cost of the refinement process. If you don’t drive your car hard and/or in extreme conditions, and if you don’t tow heavy loads or supercharge your engine, and if you change your oil promptly on schedule, the price increase to switch from conventional oil may not be worth it to you.

Early synthetic motor oil offerings were known to leak, especially when people switched back and forth between conventional and synthetic, but that is no longer a problem.

Before you decide whether you should switch to synthetic, check your owner’s manual to get your car maker’s recommendations. Switching to a type of oil that goes against recommendations could affect your warranty.

Still have questions about the right motor oil for your vehicle?

Ask a Team Member at any of our 4000 auto parts stores across the country.

Editor’s note: Advance Auto Parts offers great savings on motor oil, oil filters and more