When To Decide To Change Oil To Synthetic by: mdc1022 - Feb 26, 2020 18:46:11 GMT -6 Back to Home Reply Quote Select PostDeselect PostLink to PostMemberGive GiftBack to Top Post by mdc1022 on Feb 26, 2020 18:46:11 GMT -6 With only 35 miles on my scooter. I have a 2020 BD50QT-2A 49CC - Single-cylinder, air-cooled, four-stroke scooter.I did already change my oil. I used Castrol GTX 10W30. I would like to know at what mileage I should consider full synthetic? I was going to change to Castrol POWER1® 4T Motorcycle Oil, 10W40 I was told this is a great oil to use when I change over to full synthetic?At what mileage is it "safe" to change from conventional oil to full synthetic? Also, which oil do you like best?? It has great reviews and is formulated for 4 stroke 49 cc engines.your thoughts??and when should I change from regular to synthetic? I currently have 35 miles on my scooter and did 1 oil change yesterday.