Performing regular maintenance is one key to getting the longest life out of a car and its engine; knowing when to get the oil changed and changing the oil are vital for that process.http://www.youtube.com/watch?v=2HKqUy9zDO0   

Many oil change shops will provide a windshield sticker to remind of the next oil change, and some newer cars will alert the driver using an on-board computer. However, for situations where that is not the case, there are three things car owners can do to determine when it's time to drain that old oil and add new, including checking the mileage and time passed since the last oil change, looking at the color of the oil in the engine and feeling the oil to determine its texture.http://www.youtube.com/watch?v=2HKqUy9zDO0 

While basic rules of thumb apply to mileage and time that should go by between oil changes, these rules will vary based on the type of oil in the car.

For conventional, crude oil, get an oil change after 3,000 to 5,000 miles or three month's time, whichever comes first.

For synthetic oil, change your oil after 5,000 to 7,000 miles or waiting six months, whichever comes first.http://www.youtube.com/watch?v=2HKqUy9zDO0 

If you don't know when the last time the oil was changed in a car, the appearance can be used to determine if it's time to be changed.

Drain a bit of the oil into a clear container to look at the color. If the oil is lighter, like the color of vegetable or olive oil, this indicates fresh oil and means an oil change was likely recently performed.

If the oil is dark in color, like that of a cola or dark beer, this indicates the oil has been used and is ready to be changed.

If the oil is anywhere in between these choices, check the texture of the oil to determine if a change is necessary.http://www.youtube.com/watch?v=2HKqUy9zDO0 

1. Remove the oil dipstick from the engine.
2. Take a drop of oil from the tip of the dipstick and rub it between your thumb and forefinger.
3. If you feel any grit or friction, this indicates old oil and suggests that an oil change is necessary.http://www.youtube.com/watch?v=2HKqUy9zDO0