Vapor lock can be caused by what conditions?

• A. High altitude atmospheric pressure.
• B. Fuel can vaporize due to engine heat, local climate, or a lower boiling point at high altitude.
• C. Vapor lock only occurs in diesel engines.
• D. Vapor lock can be corrected by turning the engine main switch off.

Answer: (B)

Vapor lock happens when fuel in the lines or carburetor boils and becomes vapor, so the engine can’t get a steady supply of liquid fuel. The best explanation is that fuel can vaporize because of engine heat, a hot local climate, or a lower boiling point at high altitude due to reduced ambient pressure. When fuel boils, vapor pockets form and the fuel pump can’t move liquid fuel effectively, causing the engine to lose power or stall until the vapor dissipates. This is more likely with hot engine compartments and long fuel lines near heat sources, and the effect is amplified by lower pressure at altitude. Turning off the main switch isn’t a reliable fix and isn’t what normally clears a vapor lock, and vapor lock isn’t a typical issue for diesel engines.