What I said was: very few 30-grade DUAL RATED (API CK-4/SN) heavy duty oils also meet Ford WSS-M2C171-F1. Oils approved for API SN (Starburst or not) requires 600-800 ppm of phosphorus for 16, 20, & 30 grade oils while thicker oils (40, 50, 60-grade) only have 600 ppm lower limit. All single rated (API CK-4) heavy duty oils (including 30-grade) have 1200 ppm phosphorus upper limit and no lower limit, which is why Ford developed their own 1000-1200 ppm spec. See API: Latest Oil Classifications
