Synthetic oil is not for old engines with their original seals, says HowStuffWorks. However, in modern engines, conventional oil can be switched with synthetic oil without any problem. The higher cost versus the benefit of synthetic oil is the only real consideration.
The advantage of synthetic oil is that its molecular structure stays more stable with temperature changes and lasts longer between oil changes, states HowStuffWorks. Just make sure the engine has good seals. Unlike in the early 1970s, modern synthetic oil no longer wears down seals and creates leaks. However, its streamlined molecular structure can find cracked or marginal seals and clean out the deposits that have been plugging their leaks.
An engine that started with mineral oil can run just fine on synthetic oil, elaborates HowStuffWorks. As long as the seals are in good condition, mineral and synthetic oil can be switched back and forth, mixed, matched, blended or alternated. An engine can run on mineral oil for 3,000 miles and on synthetic oil for the next 5,000 miles. As long as the oils are the same weight, five different oils from five different manufacturers can be used.
As of 2015, the cost of synthetic oil is around six to 10 more than that of mineral oil, reports HowStuffWorks, but it is possible to use the former during the cold winter months and the latter during summer.