Measure Fuel Dilute
Diesel fuel is chemically similar to the lubricating oil used in diesel engines. Slow fuel leakage can cause fuel to mix into the engine oil. Normal operating temperatures may cause the volatile portion of the fuel to vaporize. Fuel retained in the engine oil is less volatile.
A closed-cup flash point test can be performed to detect fuel dilute. The flash point test measures the volatile portion of residual fuel in the engine oil. Detecting small amounts of volatile fuel is difficult. Insufficient evaporation reduces the accuracy of the flash point test.
Because the flash point test cannot accurately detect fuel dilute, it should not be used as the sole method for measuring fuel dilute.
Alternatively, verify dilute using the following methods:
• Gas Chromatography Fuel Dilute Test
• Engine Oil Viscosity
A gas chromatography test is used to measure fuel dilute in crankcase oil. Gas chromatography can identify minute differences in chemical composition between diesel fuel and lubricating oil. All Caterpillar regional SOS service labs use gas chromatography (GC) to measure fuel dilution. Some Cat dealerships also use GC. Even though GC provides more accurate fuel dilution measurements, viscosity testing is always used to confirm the results.
Fuel dilution significantly reduces engine oil viscosity. If unacceptable fuel dilution is suspected, the kinematic viscosity of the engine oil must be measured.
Fuel dilution greater than 4% typically results in a viscosity below the specified viscosity grade. If the engine oil still meets the specified viscosity grade, the fuel dilution may not be unacceptable. Use the table below to determine if the viscosity is at the minimum acceptable level. The viscosity values in the table are slightly below the SAE viscosity grade limits. However, these values still provide adequate engine protection.
Viscosity Grade
0W-40
5W-40
10W-40
15W-40
12.0 cSt
| 0W-40
5W-40 10W-40 15W-40 |
| 0W-30
5W-30 10W-30 |
Minimum engine oil viscosity at 100 °C, measured by gas chromatography, with fuel dilution greater than 4%.
Investigate the cause of fuel dilution or shorten the engine oil change interval.
Confirming Fuel Dilution Always combine viscosity testing with GC testing to confirm fuel dilution with a result greater than 4%. If fuel dilution testing cannot be performed locally, submit the oil sample to a Cat dealership for analysis.
Drain and refill the engine oil. Please refer to the Operation and Maintenance Manual, “Engine Oil and Filter – Change”.
Result: All injectors are normal.
Proceed to Test Step 3.
3. High-Pressure Fuel Pump Shaft Seal
A. Check for fuel leaks around the high-pressure fuel pump shaft seal.
Result: Fuel is leaking through the high-pressure fuel pump shaft seal.
Repair: The return line to the fuel tank is blocked. Investigate the cause of the blockage and then repair the fuel line.
Replace the high-pressure fuel pump. Please refer to Disassembly and Assembly, “Injection Pump – Removal” and Disassembly and Assembly, “Injection Pump – Installation”.
Replace the fuel coarse filter and fuel fine filter. Please refer to the Operation and Maintenance Manual for more information.
Replace the fuel transfer pump inlet regulator (TPIR).
Inspect the return line between the high-pressure fuel pump and the fuel tank. Replace any lines damaged or deformed by hot fuel.
Drain and refill the engine oil. Please refer to the Operation and Maintenance Manual, “Engine Oil and Filter – Change”.
Result: The high-pressure fuel pump shaft seal is normal. If the problem persists, contact the Dealer Solutions Network (DSN).
