Fuel Dilution - Lubricating Oil Analysis
Fuel dilution of crankcase oil by unburned fuel reduces lubricant effectiveness. The thinning of the lubricant can lead to decreased lube film strength adding to the risk of abnormal wear. Depending on certain variables, when fuel dilution of crankcase oil exceeds 2.5 to 5%, corrective action should be taken. Fuel dilution is measured by gas chromatography. The results are reported in percent volume.
Cause
• Incorrect air/fuel ratio
• Extended idling
• Stop-and-go driving
• Defective injectors
• Inoperative carburetor choke
• Incomplete combustion
• Incorrect timing
Effect
• Metal-to-metal contact
• Poor lubrication; oil thinning
• Increased overall wear
• Piston ring wear
• Decreased additive effectiveness
• Risk of fire or explosion
• Reduced fuel economy
• Decreased oil pressure
• Reduced engine performance
• High operating cost
• Shortened engine life
Solution
• Check fuel lines, worn piston rings, leaking injectors/seals, pumps
• Analyze driving/operating conditions
• Check spark timing
• Avoid prolonged idling
• Change oil and filter more frequently
• Evaluate equipment and use vs. design
• Check fuel quality
• Repair/replace worn parts
