Phillips 66 T5X Heavy Duty 40 is a Mono-grade heavy duty diesel engine oil. T5X Heavy Duty Oils are a mixed fleet diesel engine oil line manufactured by Phillips 66 Lubricants. These mono-grade or straight weight engine oils can be used in over-the-road diesel trucks, off highway diesel equipment, farm tractors, and passenger cars and light trucks with diesel and gas engines. This grade is particularly suited for use in Detroit Diesel 2 Stroke engines requiring low-ash formulations. 40 is the thickness of the oil based on Society of Automotive Engineers (SAE) standards. 

*This product line was formerly known as 76 T5X Heavy Duty

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