Project 2.Slow Mazda3

[ScottyB]

Doesn't oil break down and has a time? Regardless it will be changed almost every 3 months so it doesn't matter.

on the shelf? not really, you could pick up a modern synthetic 40 years from now and it would still be fine.

in use, yes an oil will break down depending on exposure to wear, heat, and moisture. heat is the biggest killer in an engine like yours.

if you're changing it fairly often you've got nothing to worry about. if it sits a lot over the winter i'd give it a good drive every month or so.