So at 67k, I shouldn't have any problems changing over to synthetic when conventional oil has been used up to this point?
Just make sure you use the same grade oil 5w20, 5w30 10w30 etc
from the manufacturer because the piston rings expand with heat to a point and the thickness of the oil makes up the rest, if you use a thinner oil
you might smoke a little since your rings are accustomed to expanding only
so much with heat. That is where the factory tolerances come into effect.