Regularly changing car engine oil is essential to ensure that the working parts of the engine are properly lubricated. Small metal particles from the engine circulating in the oil can accelerate wear, and the oil itself can lose its lubricating properties with time. Whilst changing the oil is a simple job for the home mechanic, it is vital that the oil filter is also changed to prevent blockage and engine seizure.Before draining the oil, warm the engine to operating temperature before switching off to help the oil to drain. Before draining the oil, ensure that a suitable container is placed under the sump drain screw to prevent a mess! Remove the oil filler cap to allow air to enter the sump, then locate and unscrew the sump drain screw and remove completely.Whilst the oil is draining, take a clean cloth and remove any sludge and metal deposits from the screw. The drain screw is usually magnetised to help remove metal shavings from the sump, so any deposits are normal.When the oil has drained, use an oil filter wrench to unscrew the filter, and then discard. The new filter should be filled with fresh oil prior to fitting to prevent air bubbles entering the oilways on start-up. Using the oil filter wrench, ensure that the filter is tight before refilling the sump.To prevent an embarrassing mess and a waste of oil, ensure that the sump plug is carefully refitted and tightened with the correct spanner before refilling! Use the correct type and grade of oil as recommended by the manufacturer to refill the sump to the top mark on the dipstick.