If your spark plug gets harmed or has turned black, chances are you will face trouble with the oiler and starting the engine. At the very beginning, you must read the spark plug to know what occurred. Examine the spark plug, and if it proved to be black, it could be due to one of these two reasons:-. Carbon Fouled. Oil Deposits. Generally, a spark plug is made for long use which can last up to 80,000 miles if no physical harm is done. Also, the longevity depends on the type of spark plugs and what type of BMW engine you have. Take a look at the table below to see what types of BMW engines often require new spark plugs. Brand-wise Spark Plugs for BMW Cost Chart.