What are the main differences between synthetic and dino oil?
Is one always better than the other?
A full synthetic oil, as the name states, is "synthesized". By that, they mean it is made in a lab, it is a manufactured product.
Organic (Dino) oil is a product of nature.
So the big difference is the environment in which the oil is made in.
The main selling point on synthetic over organic is because it is manufactured, it is made in a controlled environment. That means far less impurities and a more consistent product.
Organic oil will be influenced by what it was made from, what was in the ground where it was extracted from, etc.
Another way to think about it is synthetic is an additive process. They start with nothing and add in the components they want until they get the end product.
Organic oil is a reductive process, they start with an unrefined product and filter out all the stuff they don't want until they have what they want left.
It's not a case of one being unconditionally better than the other, for automobile applications. For example:
Oil still gets dirty. Syn might not break down as fast as dino and have better cold start properties etc, But engines still wear and there is still by-product of combustion that gets transferred to the oil. I would suggest changing the oil filter at 3000-3500 miles on a 7000 mile oil change with syn. On this annual change syn,same filter change interval ,3000-3500 miles. Sludge doesn't appear to be a problem with syn and it appears to offer better protection. But it's nice to have a choice.
I restored a 66 Chevelle SS with a 502 crate motor. Ran synthetic for two years burning a quart every 800 miles. Oil was black when I changed it. Ran dino for 6,000 miles at the advice of a mechanic. Oil after second change was amber and no burn. Went back to synthetic and no oil burn. Just my experience and don't mean to create a fight here. Just my experience.
Although many people do not drive there cars hard enough to need synthetic oils, being able to go 10k miles before a change makes them cheaper in the long run, though more expensive per oil change. And when living in an area where temperatures get below -20, it can really help with starting. Also if you care about the environment, they are better for it too.