In addition to lubricating the engine, synthetic and regular oils keep the various parts of the engine clean and free from obstructions by sweeping them into the filter. Eventually, however, the filter clogs and the particulates keep circulating inside the lubricant, which eventually becomes sludge.

The engine has to work harder to push this viscous sludge through the system, which means it won't be able to work as efficiently, and your gas mileage—and wallet—will suffer as a result.

Most cars come with warranties that include stipulations about keeping up with routine maintenance. Regularly scheduled oil changes are an integral part of vehicle maintenance. Failing to adhere to this standard could result in your warranty being voided.

The worst-case scenario if you go too long without getting an oil change is that your engine could seize or blow a gasket. Both problems could mean you're out a vehicle.

Blowing a gasket won't necessarily total your car, but the repairs will be costly. Depending on how old and/or valuable your car is, you might be better off scrapping it for another.

If your engine seizes, you're really out of luck. No oil means metal parts are grinding against other metal parts inside your engine, warping them irreparably. You'll need to replace the engine, which is almost invariably too expensive to be worth doing.