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Possible Causes
• Incorrect maintenance interval and/or engine oil
• Engine oil contamination
• Intake system leak
• Dirty fuel
• Low oil pressure
Recommended Actions
Note: These steps are listed below in order of probability. Perform these steps in sequence:
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1. Incorrect Maintenance Interval and/or Engine Oil
A. Use the engine oil recommended in the engine operation and maintenance manual and change the engine oil at the intervals recommended in the manual.
Result: Engine oil was not changed at the intervals recommended in the operation and maintenance manual.
Repair: Use recommended grade engine oil.
Change the engine oil at the recommended intervals. Repair or replace all damaged parts.
Result: Engine oil was changed at the intervals recommended in the engine operation and maintenance manual.
2. Engine Oil Contamination
A. Obtain an oil analysis. The analysis will determine if the oil is contaminated.
B. Check the oil filter bypass valve.
Note: If the oil filter bypass valve is open, the oil will not be filtered.
Result: Engine oil contaminated.
Repair: Determine the cause of the engine oil contamination and then perform the necessary repairs. Drain the crankcase and refill it with clean engine oil. Install a new engine oil filter. Refer to the engine operation and maintenance manual.
Result: Oil filter bypass valve open.
Repair: Replace the oil filter element.
Refer to the operation and maintenance manual.
Check if the spring of the oil filter bypass valve is soft or broken. If the spring is broken, replace it. Verify that the oil bypass valve is functioning correctly.
Result: Engine oil is not contaminated.
Proceed to test step 3.
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3. Intake system leak
Note: An intake system leak can allow unfiltered air to enter the engine.
A. Check the intake system for signs of unfiltered air leakage. Inspect all gaskets and connections. For more information, please refer to System Operation, Testing and Adjustment, “Intake and Exhaust Systems”.
Result: Air leak present.
Repair: Repair all leaks.
Result: No air leak.
Proceed to test step 4.
4. Dirty Fuel
A. Remove the fuel filter. Check the fuel filter for contaminants.
Note: Impurities such as hydrogen sulfide and sulfur in the fuel can cause acidic substances to form in the crankcase.
B. Obtain fuel analysis.
Result: Fuel contaminated.
Repair: Determine the cause of the contamination and perform the necessary repairs.
Install a new fuel filter. Please refer to the Operation and Maintenance Manual.
Result: Fuel not contaminated.
Proceed to test step 5.
5. Low Oil Pressure
Note: Low engine oil pressure can be caused by contamination of engine oil with another liquid. A high engine oil level may indicate oil contamination.
A. Obtain an engine oil sample for analysis.
B. Inspect the inlet filter on the oil suction pipe and remove any substances that may be obstructing engine oil flow.
Note: The inlet filter on the engine oil pump suction pipe may be blocked. This blockage can lead to cavitation and reduced engine oil pressure.
Note: When certain engine components show signs of wear in a short period, the cause may be a blocked engine oil passage. The engine oil pressure gauge may indicate sufficient oil pressure, but components may be wearing due to lack of lubrication. In this case, check the passage supplying engine oil to the component. For more information, refer to System Operation/Testing and Adjustment, “Lubrication System”.
Result: Analysis shows contaminated oil.
Repair: Replace the oil and oil filter.
Refer to the Operation and Maintenance Manual. Result: Inlet pipe blockage.
Repair: Clear the blockage. Confirm repair.
Result: Low oil pressure.
For testing procedures, see Troubleshooting and Repair, “Low Oil Pressure”. Repair all identified faults. Result: Oil pressure is normal.
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