Car engines, including old ones, require lubrication to work. Otherwise friction kicks in quickly and bad things happen to the engine parts. The question of which oil type should be used for an old engine – 5W30 or 10W30 — is simple to answer.
Older engines have wear and tear on them, regardless of how well they've been cared for. An oil that moves faster gets to the working parts sooner, protecting them when the engine starts. However, even with older engines, owners should follow the manufacturer's recommendations with frequent oil changes rather than guessing.
Every modern car today uses either 5W30 or the alternative, 10W30 engine oil. Older engines tended to come with 5W30 since it helped the engine run during cold weather, and it still does today. That said, engines can run on both as long as allowed by the car manufacturer.
10W30 engine oil works on almost all cars regardless of their lubrication needs. To reduce operating costs with multiple barrels of stock oil, just having one oil type on hand is far easier and cheaper for auto repair businesses.
