I just bought a 2004 silverado with 104000 on it. Can I start using synthetic oil in it?
Try using the blend first. If you don't get any oil leaks the go full synthetic. If it starts to leak oil use high mileage engine oil or fix the oil leaks then go full synthetic. HTH
Generally, the real oil will form a protective coating around the gaskets. Switching much later, 104,000 miles, to synthetic oil will dissolve that coating and the gaskets will start leaking. Rule of thumb is to start synthetic oil in a new engine only. Like tennisshoes said above, there are oils out there made for longer use engines, and it may not hurt to go to a heavier weight oil. I went from 20W-30 to 20W-50 in my Buick after 120,000 miles. I kept getting low oil pressure warning lights when starting the car. I changed oil to a heavier weight, and no more warning lights. The garage had put in 10W-30 for the hot So. Ca. summer driving.
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