What is the acceptable fuel percentage in L/O?

• A. 0-1.9%
• B. 2.0-3.4%
• C. 3.5-4.9%
• D. 5.0% and greater

Answer: (A)

Fuel dilution in lube oil weakens the lubricating film by lowering the oil’s viscosity, which can lead to increased wear and damage to bearings and pistons. Keeping this contamination very low protects the engine’s lubrication system. Therefore, the acceptable range is up to just under two percent by volume, 0 to 1.9 percent. Once the fuel in the lube oil reaches 2 percent or more, lubrication quality is compromised and corrective maintenance is needed, such as investigating fuel separation and injection issues and possibly changing the oil. The higher ranges indicate progressively unacceptable contamination levels and raise the risk of engine wear.