Diesel fuel is chemically similar to the lubricants that are used in diesel engines. A slow fuel leak will blend the fuel into the oil. Normal operating temperatures may cause volatile parts of the fuel to vaporize. The fuel that remains in the oil is less volatile.
A closed cup flash test can be performed in order to detect fuel dilution. The flash test is designed to measure the volatile parts of the fuel that are remaining in the oil. Detecting less volatile fuel is difficult. The less volatile fuel reduces the accuracy of the flash test.
Since the flash test does not accurately detect fuel dilution, do not use the flash test as the only measure of fuel dilution. Instead, verify the dilution by the following methods:
- Gas chromatograph fuel dilution test
- Oil viscosity
The test that uses a gas chromatograph is designed to measure fuel dilution in crankcase oils. The gas chromatograph 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 SOS laboratories. Some Caterpillar dealers also use a gas chromatograph. Even though the gas chromatograph provides a more accurate measure of fuel dilution, always verify the results with the viscosity test.
A significant level of fuel dilution reduces oil viscosity. If an unacceptable level of fuel dilution is suspected, the kinematic viscosity of the oil must be measured.
Fuel dilution that is greater than 10 percent will usually cause viscosity that is less than the specified viscosity grade. If the oil is still within the specified viscosity grade, fuel dilution has not reached an unacceptable level.
Verify fuel dilution by the combination of low oil viscosity and a gas chromatograph that gives a result in excess of 10 percent before investigating or servicing the engine. Ask the Caterpillar dealer to submit an oil sample to a Caterpillar regional SOS laboratory for analysis if a fuel dilution test cannot be performed locally.
- Fuel injector seals
- Fuel injector tip
Note: The procedures have been listed in order of probability. Complete the procedures in order.
| Troubleshooting Test Steps | Values | Results |
|---|---|---|
1. Fuel Injector Seals A. Check for signs of damage to the seals for the fuel injectors. |
Fuel injector seals |
Result: Injector seals are damaged. Repair: Replace any damaged injector seals. Change the engine oil. Refer to Operation and Maintenance Manual, "Engine Oil and Filter - Change". Result: All injector seals are OK. Proceed to Test Step 2. |
2. Fuel Injector Tip A. Check for signs of damage to the fuel injectors. Check the fuel injector tip for cracks or breakage. |
Fuel injector tip |
Result: A fuel injector is damaged. Replace the fuel injector. Refer to Disassembly and Assembly, "Electronic Unit Injector - Remove" and Disassembly and Assembly, "Electronic Unit Injector - Install". Change the engine oil. Refer to Operation and Maintenance Manual, "Engine Oil and Filter - Change". Result: All fuel injectors are OK. Contact the Dealer Solutions Network (DSN). |