The oil in your car’s engine serves two important functions – it lubricates the moving parts of your engine and prevents the damaging wear that occurs in dirty engines. In general, the oil in your car’s engine has two enemies – heat and cold. When exposed to heat, the components in the oil break down and can no longer do their job properly. In the presence of pronounced cold, the oil thickens and doesn’t work well until it heats up and thins to its normal consistency.

Oil can be either “regular” oil – which is the petroleum-based product we’re all familiar with – or a synthetic oil product. Synthetic oils have a number of differences that are directly related to the oil properties outlined above.

Synthetic oils generally contain more additives than regular motor oils. These additives help the oil and your engine stay cleaner longer, which allows the oil to last longer between changes. Anything you can do to keep your engine clean and functioning well will obviously prolong the life of your car. Synthetic oils also tolerate extremities in temperature better than regular motor oils.

With these advantages, it would seem like synthetic motor oils would be the logical choice for any car. However, there are some downsides to using synthetic motor oils.

Synthetic motor oils cost more than traditional motor oils. This is somewhat offset by the fact that synthetic motor oils last longer and don’t have to be changed as often. Cars using regular motor oil need oil changes about every 3,000 to 5,000 miles, while cars using synthetic motor oil only need oil changes about every 25,000 miles. However, the oil filter still needs to be changed often – about every 5,000 miles at a minimum.

In addition, the other services performed during a oil change – for example, checking the transmission and brake fluid levels – still need to be performed on a regular basis; again, about every 5,000 miles at a minimum. These regular checks can help head off expensive repairs and shouldn’t be ignored – even if it’s not time for another oil chance. The synthetic oil should also be checked regularly to make sure that it hasn’t become contaminated. For some people, not having the oil changed during these regular service checks just isn’t that great a benefit, since they have to take their cars in regularly anyways.

You may also want to take climate considerations into account when choosing between synthetic and regular motor oil. Synthetic oils have long been used by the military, since military vehicles can be subjected to incredibly wide temperature variations. A vehicle could be used in the desert heat one day and in icy conditions two days later. Synthetic oils can handle these variations without problem. However, most automobiles simply don’t experience changes in condition this extreme. Could synthetic oil offer additional protection for stop and go city driving in extremely hot or cold weather? Yes, but the additional protection offered may not be worth the additional cost.

One final consideration – your engine oil touches a number of malleable parts, like seals and gaskets. These parts swell in response to the contact with the oil. Changing your oil could cause changes in the seals and gaskets, leading to oil leaks and costly repairs. Unless you have a brand new car and want to run synthetic oil from the beginning, you’re probably better off sticking with the same oil you’ve been using.