Boiling fuel leads to vapor lock

October 1, 2008 | By Richard Prince


I recently restored a 1980 Spitfire for my granddaughter and in the process of test driving it around town for several miles it stalled at a light and would not restart. When I lifted the hood (bonnet) I noticed the fuel line filter (which I had installed) was bubbling fuel within the glass filter. After an hour or so when the bubbling stopped, I was able to restart the engine and it ran fine. I don’t have a clue as to what caused this bubbling in the fuel filter and my son, who is a professional mechanic, was also puzzled. I’m afraid to drive the car any distance for fear this may happen again. Hopefully you can give me some possible explanation as to what’s going on. I look forward to checking future issues in the event that you can help.


It sounds as though you experienced a classic case of vapor lock due to the fuel boiling. When the fuel gets too hot it boils, which is to say that vapor bubbles form in it. These effectively block the fuel from moving forward into the engine so the engine behaves as though it has run out of fuel, which in effect it has.

Make sure all components in the fuel system, including the tank, lines and filter, are as far as possible from sources of heat, especially the exhaust system parts. If it’s not feasible to put more space between exhaust parts and the fuel line or other fuel system parts then wrap the fuel system and/or exhaust system parts with insulating material. Such material is readily available from better auto parts stores, speed shops, racing suppliers and many different online vendors.