A vapor lock condition can lead to which of the following?

• A. Partial loss of fuel flow
• B. Increased engine cooling
• C. Complete blockage of fuel flow
• D. Higher octane rating

Answer: (C)

Vapor lock occurs when heat causes some of the fuel in the line to boil, forming vapor pockets. The fuel pump is built to move liquid fuel, not vapor, so those vapor bubbles disrupt the flow and the pump can’t push liquid fuel through effectively. In practice, those vapor pockets can grow and act like a barrier in the line, so the engine may be starved of fuel. When this barrier blocks the path of liquid fuel, the engine can stop receiving any fuel, effectively producing a complete blockage of fuel flow. That’s why complete blockage is the best description of what vapor lock can cause. The other options don’t fit because vapor lock isn’t about increasing cooling or changing the fuel’s octane rating, and while a partial loss of fuel flow can happen, the situation can progress to a full blockage.