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Why Should You Change Your Car’s Oil?

It can be a pain but changing your car's oil is very important!

Oil spill on the ground

Photo: Jasper Nance (Flickr)

Oil spilled on the ground can make a pretty pattern. It is important to change your car's oil frequently and carefully.

How often do you change the air in your tires? How about your brake and radiator fluids? You may need to fill them up or change them once in a while, but you don’t have to change them the way you have to change your oil.

Change The Old

You should change the water in your radiator because it gets dirty, and that’s one of the reasons to change your oil as well. But there’s another, more significant reason that old oil doesn’t work as well as new oil.

Inside your car’s engine, metal parts are constantly sliding across each other at extremely high speeds. The friction of metal against metal at that speed could generate enough heat to destroy the engine — if there weren’t oil to lubricate the metal parts and help them slide more easily.

Why Doesn’t Old Oil Work?

The long molecules of oil work their way between the metal parts so that moving metal parts never really touch each other. But those long chains don’t last forever.

Heat and the motion of the engine break down the long chains into shorter chains and those chains are broken down even more. Old oil is better than no oil and will at least keep the engine from seizing up. But as the molecule chains get shorter, the metal parts are more likely to come in contact with each other causing more wear inside your engine.

When automobile oil changes from the amber color it starts out with to the black color of old oil, that’s partly because it’s getting dirty, but it’s also undergoing chemical changes that prevent it from doing its job as well as it used to.


If you change your oil yourself, save the old oil and take it to a service station or recycling center since used motor oil is very toxic.

  • AG

    I usually enjoy your short posts, and subscribe to them via Facebook but I must say this article is not particularly well written. You say “often” without really giving an indication of what time scale or criteria you are talking about.

    Combined with the fact that today's motor oils are so much more advanced, today's cars come with maintenance minder systems, and so forth … this article is useless and potentially harmful to someone who reads your take as a seconding of their “Change oil once ever ___ months” premise.

    From the reading I have done (including results of oil analysis that people have graciously posted), synthetic motor oils can last anything from 7500-10000 miles (and more in some cases). Also note that unless we are talking about someone leaving their engine oil unchanged for several years, the main criteria is the number of revolutions of the engine's parts (not miles or time). More city driving necessitates more frequent oil changes.

    Please consider updating your post with more concrete information. -ag

  • Nick Stageberg

    Nice walkthrough, I have my own little how-to video on changing your oil here:
    Hope you find it useful!

  • Silas Knight

    I never knew the science behind motor oil, that is interesting! It’s cool to think of the oil as a chain of protecting molecules. I can see why changing the oil would be important, when you put it this way.

  • Ridley Fitzgerald

    It’s good to know why oil changes or necessary for your car. I used to think that it was just a way that car companies got money, but now I know how much my car needs new oil! It’s also good to know that oil needs to be recycled!

  • Tims Strix

    Thanks for sharing. This is helpful.

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