What is vapor lock in an engine?

Vapor lock occurs when fuel in the fuel lines vaporizes due to heat, which then creates gas bubbles that disrupt the normal flow of liquid fuel to the engine. This condition can result in engine performance issues, such as misfires, stalling, or difficulty starting, particularly in high-temperature conditions. Since gasoline is more susceptible to vaporization under certain conditions, maintaining fuel flow is essential for optimal engine operation.

The other choices focus on different types of issues that do not accurately describe the specific phenomenon of vapor lock. For instance, a filtration issue concerns the cleanliness and flow of fuel into the engine rather than the state of the fuel within the lines. A temperature malfunction in the engine block refers to problems with engine cooling systems affecting engine temperature rather than the fuel delivery process. Similarly, a cooling system failure impacting fuel delivery does not directly relate to the vaporization of fuel in the lines itself, which distinctly characterizes vapor lock.