My wife is looking at cars. She found one she likes- A Mazda 3. The owners started putting Synthetic Oil in it about 2 or 3 years ago- Is it OK to switch over from regular to Synthetic Oil? If so, is it OK to then switch back to regular oil after having used synthetic for a while?
Yes, you can switch back and forth as often as you like. No damage will result. The engine doesn’t care which oil you use.
Unless the owner’s manual specifies synthetic there’s really no advantage to using it.
Thanks- Your advice is appreciated. The guy who has been doing it seems to think it may improve his mileage- I don’t understand that idea.
When synthetic first came out, mixing as a bad idea. Today the available products don't have that problem so you can switch back and forth as much as you like as long as you meet all the specifications listed in that Owner's Manual.The difference would be too small to measure.