Section 1065.735 - Diesel exhaust fluid(a) Use commercially available diesel exhaust fluid that represents the product that will be used in your in-use engines.(b) Diesel exhaust fluid for testing must generally conform to the specifications referenced in the definition of "diesel exhaust fluid" in § 1065.1001 . Use marine-grade diesel exhaust fluid only for marine engines.81 FR 74191, Oct. 25, 2016