vapor lock

[1] This is an unwanted condition where bubbles of air form in the fuel line caused by boiling or vaporizing of the fuel in the lines from excess heat. The boiling will interfere with the movement of the fuel and the air bubbles which form will in some cases, completely stop the flow. Sometimes it will cause the float chamber to overflow which floods the carburetor and result in an over-rich mixture that can cause stalling of the engine when the accelerator is depressed. Fuels containing alcohol have lower boiling points and many old-car owners have installed more-powerful electric fuel pumps which overcome vapor lock tendencies of these fuels by pushing them through the air bubble. A wet rag will cool the line and get rid of the problem. To prevent the problem in hot weather, some mechanics wrap tinfoil around the fuel lines to reflect the heat away.

[2] The abnormal condition that occurs when brake fluid contains too much moisture and is overheated, causing the moisture in the fluid to boil. Gas bubbles are formed in the fluid, which causes a spongy brake pedal or a complete loss of hydraulic pressure.

[3] Condition where liquid is trapped in line because of bend or improper installation. Such vapor prevents liquid flow.