GUARD AS 6S8021 - Caterpillar

Introduction
The problem that is identified below does not have a known permanent solution. Use the solution that has been identified below until a permanent solution is known.Before you perform any procedure in this Technical Information Bulletin (TIB), ensure that you have read the information and that you understand the information that is contained in this instruction.This TIB includes the recommended method for determining fuel dilution of the engine oil. Additionally, the probable causes and the recommendations for correcting the fuel dilution are provided.Problem
Diesel fuel is chemically similar to diesel engine oil. A slow fuel leak will blend the fuel into the oil. Normal operating temperatures may cause volatile parts of the fuel to vaporize in the engine and then leave the engine. The fuel that remains is less volatile.A closed cup flash test is sometimes used to detect fuel dilution by measuring the volatile parts of the fuel that are remaining in the oil. Detecting the less volatile components of the fuel that are left behind in the sump is more difficult and the accuracy of the flash test is significantly reduced.Solution
The flash test should not be used to detect fuel in oil. This method will not be accepted as a valid fuel dilution test. Instead, verify the dilution by the following methods:
Gas Chromatography
Oil ViscosityThe gas chromatography method is designed to measure fuel dilution in crankcase oils. The gas chromatograph instrument can identify the small chemical differences between diesel fuel and lubricating oil. A gas chromatograph is used to measure fuel dilution at all Caterpillar regional S O S Service labs. Some Caterpillar dealers also use a gas chromatograph. Even though the gas chromatograph provides a more accurate measure of fuel dilution, oil viscosity should factor into determining future actions and engine maintenance.A significant level of fuel dilution reduces oil viscosity. If an unacceptable level of fuel dilution is suspected, the kinematic viscosity of the oil at 100° C (212° F) must be measured.Fuel dilution that is greater than four percent will usually cause viscosity that is less than the specified viscosity grade (example: 15W-40 oil with four percent fuel dilution will have a viscosity of less than 12.5 cSt). 2007 EPA mandated on-highway engines have been found to have a higher fuel dilution level than previous models and condemnation limits for fuel dilution have been changed to address these trends. Use the following chart to determine engine maintenance and/or actions associated with fuel dilution. The guidelines for fuel dilution in the chart are slightly different than previous published values. However, these guidelines still provide adequate protection for these on-highway truck engines.
Table 1
Viscosity Grade Oil Viscosity at 100°C (cSt) Fuel Dilution (%) by Gas Chromatograph Action    
15W-40     Greater than 11.5 cSt     Less than 6 percent     No Action Required    
15W-40     Greater than 11.5 cSt     Greater than 6 percent     Continue sampling. Reduce the oil drain interval by 5 percent.    
15W-40     Less than 11.5 cSt     Greater than 6 percent