i can use conventional oil once in a while when mostly using synthetic -honda accord 2006
because if i change the synthetic oil at canadian tires, after subtract the coupon value, it is about the same price as i change systhetic oil at my mechanics shop, so it is not bother.
either i change conventional oil this time for 10$, or just discard rhe coupon and change at my mechanics , for about 70$
i would like to make sure if i change conventional oil, any harm? or it is just not worth it?