Recently picked up a 1999 SC300 recently with 60,800 miles. Now has 65,900 and its time for an oil change. From what I understand the car has been serviced exclusively at the lexus dealer, so my best guess is synthetic blend has been used for most its life. Is there an approximate milegage or age range when swithching to full synthetic is actually a negative on these cars?

 

your car is already very young, so i would go ahead and put some synthetic oil in there.

 

Synthetic oil doesn't effect the car enough unless you have oil sludge built up in side the motor from lack of maintence. If your car burns oil when it gets over 100k switch to thicker oil like 10w-30. Some people take the full synthetic oil to the extreme its funny. Do your oil changes on time and you shouldn't have any issue. Your just going to be paying more for full synthetic ,but go ahead and be my guest lol.