Does it ruin the engine if I switch from regular oil to the synthetic?
Not at all just change the oil filter too. Mobile 1 is my pick.
Won't hurt a thing. You can switch back and forth with no issues. I also like Mobil1.
..unless it has an oil leak, it would get worse
Looking for a Used Corolla in your area?
CarGurus has 54,506 nationwide Corolla listings starting at $1,200.
Search Toyota Corolla Questions
Toyota Corolla Experts