Engine oil provides lubrication for—and conducts heat away from—internal engine components.
Manufacturers differ in their recommended guidelines for oil and oil filter changes. As a general rule though, engine oil should be changed every 3,000 miles to keep the engine healthy and to prolong its life.
When changing or adding engine oil, follow the manufacturer's recommendation for the grade, often referred to as "weight" (0/30W, 5/30W, 20/50W, etc.), and type (petroleum or synthetic base) of oil to use. The grade based on the oils ability to flow - "viscosity". Using an incorrect type or grade may invalidate your manufacturer's warranty.
To change the oil, the technician removes the drain plug at the bottom of the engine oil pan and drains the oil. Then, the drain plug is re-installed and the engine is filled with fresh oil. The engine is started and checked for leaks. Finally, the engine is switched off, the oil level rechecked, and the maintenance light reset.
Mechanics' Corner: More Technical Detail
Most manufacturers have now included panels that are attached to the vehicle's underside; they offer a measure of protection from debris and a means of controlling air flow to the engine and around the vehicle. These panels often completely cover the engine/transmission from below, blocking all access. Removal of one (or more) of these panels and their correct re-installation adds two new steps to the process of an oil change.