Diesel Fuel In Used Engine Oil Samples

By BRETT WINBERG & VISGAGE

During winter months, most of us start our vehicles and let them idle to warm up vital components. For instance, in some cases, engines must idle to allow a PTO pump to warm up before operating, or a crane to warm to operating temperature before lifting and a fuel truck to warm up before filling fuel storage tanks. However, there is a downside… excessive fuel can digress to the oil system through leaking injectors, seals, fuel fittings, pumps or incorrect choke adjustments. Fuel dilution problems can also increase due to poor combustion characteristics.

These tables below allow you to determine an abnormal to critical fuel dilution level.

TABLE FOR DETERMINING APPROXIMATE FUEL DILUTION OF DIESEL LUBRICATING OIL KINEMATIC CENTISTOKES AT 40° C

NOTE: TABLE IS BASED ON A FUEL OIL VISCOSITY OF 3.0 AT 40°C

This tabulation may be used to determine the approximate percentage of fuel oil contained in a sample of used diesel engine lubricating oil. This assumes the kinematic centistoke viscosity is at 40° C of the used oil… and the same is known of new oil.

To use this chart, pick the column headed by the viscosity nearest that of the new oil. In that column, find the viscosity nearest that of the used oil sample, and in the same horizontal line… in the outside columns (headed "fuel oil dilution") is given the percentage of fuel dilution.

Viscosity of the used oil sample may be determined in the laboratory by a standard kinematic viscometer, or it may be obtained with sufficient accuracy by the use of a portable viscometer. The viscosity of the oil when new may be obtained in the same way, or taken from the supplier's specification.

Example: a sample of used oil is found to have viscosity of 137 CST. at 40°C. the oil when new had a viscosity of 160 CST. at 40° C. In the column headed by 160 CST., a viscosity of 137 CST. lies in the horizontal line corresponding to a fuel dilution of three percent.

TABLE FOR DETERMINING APPROXIMATE FUEL DILUTION OF DIESEL LUBRICATING OIL SAYBOLT UNIVERSAL VISCOSITY AT 100° FAHRENHEIT

NOTE: TABLE IS BASED ON A FUEL OIL VISCOSITY OF 37 SEC. SAYBOLT UNIVERSAL AT 100°F.

This tabulation may be used to determine the approximate percentage of fuel oil contained in a sample of used diesel engine lubricating oil if the Saybolt second viscosity at 100 degrees F of the used oil… and the same is known of new oil.

To use this chart, pick the column headed by the viscosity nearest that of the new oil. In that column, find the viscosity nearest that of the used oil sample, and in the same horizontal line, in the outside columns (headed "fuel oil dilution") is given the percentage of fuel dilution. Viscosity of the used oil sample may be determined in the laboratory by a standard kinematic viscometer, or it may be obtained with sufficient accuracy by the use of a portable viscometer as well. The viscosity of the oil when new may be obtained in the same way, or taken from the supplier's specification.

Example: A sample of used oil is found to have viscosity of 755 sec. at 100°F. The oil when new, had a viscosity of 850 sec. at 100°F. In the column headed by 850 sec., a viscosity of 755 sec. lies in the horizontal line corresponding to a fuel dilution of two percent.

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