API CI-4 oils that also carry the classification CI-4 PLUS are formulated to provide a higher level of protection against soot-related viscosity increase and viscosity loss due to shear in vehicles powered by diesel engines. As of September 1, 2004, oils that meet the requirements for API Service Category CI-4 PLUS and that are properly licensed may display “CI-4 PLUS” in the lower portion of the API Service Symbol in conjunction with API Service Category CI-4 in the upper portion.

Oils that satisfy API Service Category CI-4 PLUS are superior in performance to those meeting API CF-4, CG-4, CH-4 and CI-4, and can effectively lubricate engines calling for those Service Categories.

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