They rate 229.3 for longer drain intervals (in newer cars) and slightly improved fuel efficiency (0.5-2%) over 229.1. Its unlikely that you'll see a 15w-50 that's 229.3 or 229.5 Mobil 1 15w-50 works very well and is readily available at a reasonable price. The Lubro Moly 5w-40 is excellent also, but is usually significantly higher priced.

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Brian Toscano