Would changing oil from Conventional to Synthetic (for about a year) and then changing back to Conventional do any harm for the engine??

 

What is the mileage on your car? If you have more than 100k on the motor, and it has had no history of using synthetic, you don't want to put synthetic in. It would be detrimental to the motor as the the synthetic will clean out oil buildup seals and you'd be leaking oil like a ****. Just stick with something like Castrol GT-X 10w-30. That would benefit the car just fine. Also don't use the high mileage oils....they really don't offer any benefit. I tried it an notice nothing. Doesn't warrant spending the extra money on it.

S