Is Synthetic Motor Oil Right For Your Used Car?

by Don Elliott on June 15, 2011

Choosing the right motor oil for your used car seems like a simple decision. However, a quick trip to your local auto repair parts store will provide you with a wall of choices—different brands, SAE ratings, petroleum oil, synthetic oil and blends.

Basic motor oil is easily defined. Its purpose is to provide a lubricating film between the moving parts inside an internal combustion engine. One important measure of engine oil is viscosity, or thickness. Oil must coat the engine parts but also be able to flow to carry off particulates and heat. To enhance performance, motor oil manufacturers add detergents to keep the engine clean, corrosion inhibitors to minimize rust, alkaline neutralizers and anti-wear additives. Without doing some homework, the oil choices can be intimidating.

Synthetic motor oil provides an additional bit of confusion when deciding which oil to use. The Germans first developed man-made lubricants during WWII for military use during the oil shortage. Synthetic oils perform the same function as petroleum oil except they don’t break down as fast at high and low temperatures. Synthetic oils are generally “thinner” than petroleum oils. Therefore, they are preferred for high-performance engines. Because synthetic oils are made in a controlled environment, the designer molecules tend to be more consistent yielding better lubricating qualities.

What’s the trade off? Synthetic motor oil costs more than petroleum oil. The oil manufacturers promote better gas mileage, no special oil filter requirement, more horsepower, and a “smoother cooler-operating engine” with their synthetic oil products to justify the additional cost.

The American Petroleum Institute (API) tracks engine oil standards and additives, making it fairly easy to track various oil products. For the most part, synthetic oil and petroleum oil can be compared side by side.

“Blended” motor oils mix synthetic and petroleum oils at a ratio that is 25% or less synthetic oil. Higher ratios would require additional testing for API certification, a cost that the oil manufacturers avoid. Blended oils are often recommended for high mileage engines, providing the lubricating qualities of synthetic oils with the viscosity of petroleum oil. Mixing your own synthetic and petroleum oil is theoretically okay, as long as the standards are similar. However, why bother mixing your own? It makes sense to stick with a consistent lubrication routine with products designed for your engine.

Following the auto manufacturer’s recommendation for the proper motor oil is the safest choice for maintaining your used car value. In general, once you make the switch to synthetic motor oil, it is best to use it consistently. This will help achieve the maximum performance expected from the more expensive product.

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