Fuel lines heated by the engine bay or exhaust can cause gasoline to boil, turning it from a liquid into a vapor. Mechanical fuel pumps are designed to move liquid and cannot pump vapor, causing the engine to starve for fuel, stumble, or stall completely. This condition primarily affects older carbureted vehicles with low-pressure fuel systems.
Heard on the job
She stalled out on the grade because the exhaust was too close to the hard line and caused vapor lock.
Insider tip
Wrapping the steel fuel line in heat shielding or switching to a high-pressure electric fuel pump usually cures chronic vapor lock.
Also heard as
- vapour lock