The oil pan of your car might be leaking because the washer wasn't replaced on the drain plug after you had your oil changed. In this case, the drain plug may have been over-tightened, causing damage to the oil pan. Here's how to fix it.

  1. Remove the oil plug and drain out all the oil from the oil pan into a basin.
  2. Place a Sure Seal regular or oversized drain plug in the drain hole, over a rubber O-ring (gasket). You may need to use a thread tool to re-shape your oil pan's damaged threads. Screw in the new plug, being careful not to over-tighten it.
  3. Pour fresh oil into the oil filler tube in your engine compartment. Check your owner's manual to find out how much oil your car needs.
  4. Check to see if any oil is leaking [source: Cortes, Sure Seal].

If the oil pan's gasket is leaking, you may have to replace the gasket. Here's how to do this:

  1. Park the car on level ground.
  2. Place a basin underneath the oil pan and loosen the drain plug with a wrench. Always wear heavy work gloves while doing this so you don't get burned.
  3. Remove the oil plug and drain out all the oil. You'll know all the oil is out when a full minute passes without a single drop of oil falling.
  4. Remove any car accessories that are in the way of accessing the oil pan.
  5. Find and remove all the oil pan's bolts, using your owner's manual as a guide.
  6. Remove the oil pan.
  7. Clean the oil pan with solvent.
  8. Inspect the pan for cracks.
  9. Install the new gasket according to the package instructions.
  10. Replace the oil pan, all the bolts and all the car accessories that you removed.
  11. Pour in fresh oil.
  12. Start the engine and let your car run for a few minutes.
  13. Turn the car off and check for leaks. If there's a leak, tighten the drain plug and check again. If there's no leak, your oil pan is fixed [Source: Morr].

If you cannot find the source of the leak, you may have to put in a new oil pan. You may want to ask a car service professional to do this.