Finding the correct motor oil is a simple task, if you are armed with the correct information. But there are serious pitfalls that you must avoid.

Shopping for motor oil should be a straight forward task, but we see mistakes made all the time and often by people who should know better. We find that even some experienced mechanics will occasionally employ “guesswork” and choose a motor oil that is incorrect for their application. Choosing a premium brand or upgrading to synthetic oil will not gloss over a misapplication.

Examples of mistakes include:

  • Putting gasoline engine oil in diesel engines.
  • Not using the prescribed viscosity or grade.
  • Choosing the wrong motor oil specification for the engine.

While these missteps may not cause instant engine failure, they can lead to problems over time. If you follow the steps below, you will never make a mistake when shopping for a motor oil. HINT: The first 2 steps are the most important. Steps 1 and 2 will get you in the ballpark, while the remaining steps will help you refine your choices.

Step 1. Choose The Correct Engine Oil Specification

This is the most important aspect of choosing an engine oil. Your owners manual will offer the correct industry specification for your car such as those from the API (American Petroleum Institute) and this spec will be clearly marked on the motor oil label. This could be API “SN” for passenger cars or API “CJ-4” for diesel trucks. European cars often have manufacturer specifications such as Volkswagen “502 00” or BMW “LL-04”.

For older vehicles, the engine oil specification may be obsolete and replaced by a newer specification. If your vehicle is a little older, perform an internet search to see if the motor oil spec suggested for your vehicle has been superseded by a newer spec. Often times, newer oil specs are “backward compatible” with older specifications.

Step 2. Choose The Correct Grade

The “grade” refers to the viscosity suggested by the engine manufacturer such as “5W-30” or “0W-20”. Occasionally consumers will choose a viscosity that they feel is best with reasoning such as, “dad always used 10W-30” or “my cars have always used 5W-30, so why go with 5W-20 in my new car?” There is never a good reason to try overruling the engine oil grade suggested by the manufacturer. Just go with the grade listed in your manual and you will not go wrong (we promise).

Step 3. Should I Buy A Cheap Or Expensive Engine Oil?

Like everything else, you get what you pay for when it comes to buying motor oil. Just because two oils meet the same industry specification, doesn’t mean that they are equal in quality. The industry specs tend to be a minimal standard. There are many components that make up a motor oil and some of these additives tend to be very expensive. Motor oil makers can scrimp on some of these components to increase profit margins or lower the price. Or they can go all out and make an expensive, high-end product.

If you value the engine you are servicing, avoid the really cheap route. Many will justify buying cheaper oil by telling themselves that they’ll just change it more often. What this logic may bring is a mediocre performing motor oil throughout its service life. As motor oil is inexpensive relative to overall car maintenance costs, going the el cheapo route is not sound logic.

Step 4. Should I Choose Synthetic, Semi-Synthetic Or Conventional Motor Oil?

If you are confused about these choices, don’t feel bad. Motor oil categorization and labeling is not regulated, so some products that are listed as “synthetic” or “semi-synthetic” may not be any better than a conventional motor oil. We touched on the murky world of motor oil classifications in a recent post.

In most cases, don’t even bother with “semi-synthetic” or “synthetic-blend” motor oils. These so-called blends can contain as little as 10% synthetic oil and this tiny portion may not even be what would be considered a true synthetic oil by purists. Synthetic-blends are generally an excuse to have an inflated price tag and are unlikely to offer much in the way of real-world benefits.

As for full synthetics, the quality of these can vary wildly between brands. Less expensive synthetic oils are generally no better equipped than conventional oils. If you are going to spring for synthetic oil, stick with a reputable brand. The market is littered with over-priced synthetic motor oils that don’t even pretend to offer anything special.

As we are purveyors of ultra-high-quality synthetic motor oils, we are biased to be sure. But in our opinion, there is little reason to use conventional oil in this day and age. Its limitations when dealing with climate extremes, friction reduction and engine deposits pale in comparison to quality synthetic oils. Even for moderate everyday driving, a good synthetic oil offers vastly better engine protection.

Step 5. What About Aftermarket Oil Additives?

They can be called oil additive, oil stabilizer, oil treatment, oil supplement or tune-up-in-a-can and the vast majority are a complete sham. Most do nothing and some can actually be harmful. Most of these products exist to convince you that you are doing some good for your engine, but their real function is to separate you from your money.

Some motorists buy the cheapest motor oil they can find and then add these expensive products thinking that they have created a winning formula for their engine. If you have a good functioning engine, avoid aftermarket oil additives and save your money. Simply choose a good quality motor oil and that is all you will ever need.

The one product that can be effective to add to motor oil is engine flush products. Engine flushes are generally added just before the oil is changed and can be effective at cleaning out harmful engine deposits. Regularly serviced engines would rarely need an engine flush.