Synthetic, semi-synthetic or mineral: does it matter?
The base oil sets the ceiling on what an oil can do. On a modern engine there is usually only one honest answer.
What the labels mean
Mineral oil is refined crude. Synthetic is built from more uniform molecules, either heavily processed mineral stock or fully engineered esters and PAOs. Semi-synthetic is a blend. The practical difference is stability: how well the oil holds its viscosity when hot and how long the additives survive.
Where synthetic genuinely wins
Cold starts, turbochargers and long intervals. A synthetic oil pumps faster below freezing, resists coking on hot turbo bearings, and degrades more slowly across 15,000 miles. Any engine with a turbo, a DPF or an extended service schedule effectively requires one.
When mineral is still correct
Older engines specified for 10W-40 or 15W-40 were designed around thicker mineral oil, with seal materials and clearances to match. Switching a high-mileage engine to a thin synthetic occasionally reveals leaks the thicker oil was bridging. If the handbook says mineral, mineral is fine.
How to decide in the aisle
Ignore the words on the front and check the approval on the back. If the oil carries the specification your engine requires, its base-oil marketing is irrelevant, because no mineral oil can pass a modern approval test in the first place.