Changing the gearbox oil in a car can help save on wear and tear on the engine and can even improve the car's performance. A car's oil provides protection for the internal workings of your engine by thinly coating surfaces that are prone to friction. Changing the gearbox oil in a car is actually fairly simple and can quickly and easily be accomplished by any home mechanic.
Park the car on level ground and set the parking brake. If the car is too low for you to slide underneath the engine compartment, drive the car up on a set of wheel ramps and again put the car in Park. Crawl under the car and locate the bottom of the oil pan, which is the rectangular-shaped metal portion of the engine normally located toward the front of the car's engine compartment.
Find the drain plug on the oil pan and then use an appropriately sized crescent wrench to unscrew the drain plug.
Slide an oil catch pan under the oil drain plug and allow all of the oil to drain out of the oil pan into the catch pan. When you are sure all of the oil has drained out, screw the oil drain plug back in with the crescent wrench.
Locate the oil filter on the upper portion of the engine block and use an oil filter wrench to unscrew it from the engine. Screw the new oil filter into place, tightening by hand, as a wrench can overtighten the filter and damage the seal.
Pop the car's bonnet and unscrew the oil fill plug on the top of the engine. Pour the manufacturer's recommended amount of oil into the engine and then screw the cap back on tightly. Start the car up, allowing it to warm up for a few minutes, and then check the oil gauge to make sure it is in the normal range.
While there are varying reports on how often to change the oil in a car, as a general rule of thumb most newer cars (post 2000) should be able to go 5,000 miles between oil changes. Older cars may be required/recommended to have more frequent oil changes, such as every 3,000 miles or every three months.