What is used to fill the line between a fuel pressure gauge and the fuel metering system?

• A. Water
• B. Alcohol
• C. A light oil such as kerosine
• D. Diesel fuel

Answer: (C)

The line between a fuel pressure gauge and the fuel metering system is filled with a light hydrocarbon oil to purge air and provide lubrication. Using a light oil like kerosene helps ensure the line stays primed, so the fuel pressure reading isn’t spoiled by air pockets. It also lubricates the moving parts in the metering assembly, allowing smooth operation of valves and plungers that control fuel flow. Water would cause corrosion and ice issues and wouldn’t provide lubrication; alcohol can attack elastomer seals and attract moisture; diesel is usually too viscous and not compatible with many light fuel metering components.