There are two main criteria to pay attention to when it comes to selecting motor oil:

• Viscosity (often referred to as weight)
• Synthetic vs non-synthetic



First of all, if you’re under warranty, always follow the terms of the warranty, which may specify the type of oil to use.

Second, even if you’re not under warranty, you should follow any recommendations your owner’s manual makes in regards to oil. Some cars require either conventional or synthetic, and this will be specified if that’s the case.

However, with things like viscosity, there are sometimes reasons to deviate a little, and we’ll explain why below.

Why is viscosity important?

Viscosity, as you probably remember from science class, refers to the thickness of liquid matter. When it come to motor oil, the viscosity is expressed in two numbers, such as 5W-20 or 10W-30.

Lower numbers mean a lower viscosity; in other words, the substance will be “thinner”. Think of high oil viscosity ratings as syrup, and lower ones as water.

The first number represents the viscosity at winter temperatures, and the latter represents the viscosity at typical engine operating temperature. In especially cold weather (say, 0 degrees Fahrenheit or lower), your engine will run sluggishly with high viscosity oils. This is the one situation where your average consumer may actually need to deviate from the recommended viscosity. In this case, you would only want to deviate on the first number, and never by much.

The function of motor oil, after all, is to lubricate the components in your motor by working through the motor and leaving a film on each component. If the oil is too thin, the coating won’t be sufficient for protection. If the oil is too thick, it won’t work its way through all the moving parts fast enough, leaving components unprotected at times.

You should never deviate from the second number, because, again, that’s the viscosity for engine operating temp, and a majority of your driving will be with the vehicle running at temp. Thinner oils will heat up faster, which can compound the thinning effect. Thicker oils will leave the components of your engine exposed to wear and tear when the potential for wear and tear is highest.

Is synthetic oil a good investment?

Some vehicles require either conventional or synthetic oil, but most vehicle owners will be able to decide for themselves.

Synthetic oil is a more expensive oil, but this article by Nerd Wallet declares that it’s worth the price because you get more mileage out of your vehicle.

Some sources will also tell you that you can run for longer between oil changes with synthetic. We’d like to emphasize here , yet again, that you should always abide by the terms of your warranty. However, if your vehicle is no longer under warranty, it’s up to you decide if you’re comfortable testing the limits.

Synthetic oils have some of the compounds that occur in conventional oils removed, and they also have some extra things added for performance. The result is an oil that’s designed to offer better protection at extreme temperatures and result in less sludge build-up – both of which are great for reducing wear and tear on your motor.

Does the brand matter?

Motor oil manufacturers claim to have specially engineered formulas for their oils, but popular brands all meet standards set by the Society of Automotive Engineers. Only buy oil with the “SAE certified” badge on the bottle.

Auto enthusiasts and mechanics sometimes have a preferred brand. If somebody you trust can adequately explain why one specific oil is better than the rest, that may be reason enough for you. But that needs to be weighed against price differences. You might save multiple dollars per quart between different brands.

At the end of the day, just remember that the following things all matter infinitely more than the brand:

• using the right viscosity
• changing your oil on time
• keeping the oil level at full – not under-full, not over-full