When synthetic oil started gaining popularity, it was thought that it would be bad for your engine to switch between it and regular oil. It is now believed that not only is switching harmless, in some circumstances it may be advantageous.
Conventional oil is derived from crude oil, which has been refined to remove impurities. Purely synthetic oil has no base in crude oil.
Many brands of motor oil that claim to be synthetic are actually extremely refined versions of conventional oil with synthetic additives.
It was previously believed that if you used conventional oil but switched to a synthetic it would cause deposits in the engine to become dislodged and clog your engine, but this is not true.
The original concern with switching from conventional oil to synthetic was that it would cause the seals on the engine to leak. However, today's seals are much more technologically advanced and will not have leaking problems with synthetic oils.
If you drive an older car, from the 1980s or earlier, with original seals, there may still be leakage issues with synthetic oils.
Because synthetic oil is thinner, it warms up faster and can give your car extra protection during the winter if you live in a cold climate.
