For your 2005 Harley-Davidson 1200 Sportster Custom, the recommended oil capacity, as stated in the manual, is 3.6 quarts (or 3.4 liters) when performing an oil change with a filter replacement. This value is provided by the manufacturer as a guideline to ensure the engine receives the appropriate amount of oil for optimal performance and lubrication.
If you added around 2.5 quarts of oil and the oil level appears full on the dipstick, it is possible that the oil level is within an acceptable range. However, it's always a good practice to follow the manufacturer's recommendations and add the recommended amount of oil to ensure proper lubrication of the engine components.
If the oil light turns off after adding 2.5 quarts and stays off while the engine is running, it suggests that the oil level is sufficient. However, it's important to note that the oil light turning on and off with the key does not necessarily indicate the actual oil level. The best way to determine the correct oil level is by using the dipstick and ensuring it falls within the recommended range indicated in the owner's manual.
If you have any concerns or doubts about the oil level or the functioning of the oil light, it's recommended to consult a qualified mechanic or Harley-Davidson dealership to ensure your motorcycle is properly maintained.