Some car owners often weigh the pros and cons of using either synthetic or conventional motor oil in their vehicles. The truth is that for most drivers, if your vehicle manufacturer recommends using synthetic oil, then you shouldn't avoid it. A brand new or recently rebuilt engine that's still in the break-in period may not need synthetic motor oil. Some drivers believe that synthetic oil can cause leaks or other problems in older vehicles, but modern synthetic oils are designed to meet the same industry standards for engine compatibility as other oils. Synthetic oils will not damage engine seals or cause blow-by in older engines, and they may even benefit some older engines because they aren't as likely to form sludge as they break down.