The difference between synthetic and mineral motor oil

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Motor oil being poured into an engine via a funnel.

Don't just change your engine oil with any oil weight and grade. Follow manufacturer specs, with an eye toward weather. (Photo Credit: CC BY-SA/Dvortygirl/Wikipedia)

You know it’s important to change your engine oil at regular intervals. In general, the older the vehicle, the more often the motor oil should be changed. However, what do the numbers and letters listed on that container of engine oil actually mean? With assistance from The Engine Oil Bible, Car Deal Expert helps you choose the right motor oil for your car.

Why your engine oil needs regular changing

Engine oil lubricates the metal surfaces of your car’s engine. Without proper lubrication, friction buildup causes the parts to grind together and tear apart during the transfer of heat from the combustion cycle. Oil also helps clean away the chemical by-products of the combustion process and minimizes oxidation. Throughout this process, it becomes dirty and thins out, hence the need for regular replacement.

What the numbers and letters mean

Consumer motor oil is divided into three types: fully synthetic, semi-synthetic and mineral (standard) oil. Take 5W-30 motor oil, for instance. It’s a semi-synthetic blend. The number before the W is the “cold” viscosity rating of the oil, while the latter number is the “hot” viscosity rating. The lower the cold number (W stands for “winter”), the easier it is for your car’s engine to turn over when you attempt to start the car in cold climates.

Mineral oil is cheapest

Standard motor oil is effective at protecting your engine. It’s also cheaper than semi-synthetic and synthetic oil. However, it must be changed more often, as it becomes dirty and thins out more quickly.

Semi-synthetic motor oils are derived from standard oil

Semi-synthetic motor oil is closely related to standard mineral motor oil. Semi-synthetics are primarily made of polyalpholifins, writes The Engine Oil Bible. That comes from “the purest part of the mineral oil refraction process.” Thus, semi-synthetic can be mixed with standard motor oil without causing the car’s engine to seize.

Pure synthetics for heavy gearboxes

Pure synthetic oils (aka polyalkyleneglycols) are most often used for industrial purposes in vehicles with heavily loaded gearboxes. It’s high-performance stuff. Finely tuned via molecular recombination, fully synthetic motor oil can’t mix with other oils. For consumers who wish to use pure synthetic oil in their engines, said engines should be newer and in fully working order – clean with no leaks. Pure synthetics tend to break off engine deposits and leave them floating in the engine. The Engine Oil Bible suggests that once you go synthetic, you don’t go back to mineral unless you know what you’re doing.

Go with quality, lightweight oil

Choose engine oil that meets the demands of your environment. Modern engines function well with lighter, thinner oils. Consult your vehicle’s owner’s manual and ask for the opinion of a trusted mechanic.


The Engine Oil Bible

A quick rundown of synthetic vs. regular motor oil

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