Why is synthetic oil not recommended for older engines?
There is no reason synthetic oil cannot be used in an engine, regardless of mileage. Different brand oils use different additive packages and switching brands of oil, whether synthetic or conventional can lead to oil consumption. That aside, with well maintained older engines there should be no problem whatever. With engines that have not been well maintained, the detergents in synthetic oil can remove crud that is temporarily concealing oil leaks, and reveal leakage. When changing to synthetic oil I have also found it is wise to replace the oil filter, about halfway through the change cycle. This can help prevent any sludge that is being removed from plugging the filter. For instance, replace the oil with synthetic, drive say 1,500 miles and replace the oil filter. Top off the oil and then replace oil and filter at the normal change interval. A more detailed article on synthetic oil is in our Detailed Auto Topics section under Should I Use Regular Or Synthetic Oil.
