fuel vapor in fuel line?

[ymountainman]

Hey guys can you tell me at what temperature gas boils at? I have a 76f100 with the original fuel line coming from the tank. It runs along the frame rail pretty close to my headers, to the pump and up to the carb in front of the motor. The line gets HOT i think fuel has to be changing state on me. I just splashes a little in the filter. I checked the line its not stopped up and the vent is open. Im thinking about insulating it. What do yall think?

[machoneman]

That actually is a tough one to answer. Gas as we know it today comes in so many forms (winter/summer blend in many states, pure gas w/o any ethanol, 10% ethanol laden gas, E85 which I doubt you run, etc.).  Trying to measure actual real time underhood temps under varying day/night conditions is a bear as well. 

No harm in isolating fuel lines from heat, using wraps on the lines, changing gas stations (less ethanol is better) using a metal or wood heat shield under the carb. One great way to tell if heat is the real issue is to wait for a cool evening and drive it a bunch qt highway speeds, give it a 20-30 minute heat soak (engine off while hot) and see how easy/hard it is to re-start and how it handles a hot take-off and high speed run for a few miles. 

Note as well that an old and weak fuel pump can cause near-identical run issues as hot gas!

[jayb]

When I had a fuel boiling problem in my Mach 1 several years back, I measured the temperature of the float bowl of the carb with one of those infrared thermometers.  I was very  surprised to find that the fuel was boiling when the float bowl was only 165 degrees!  This was with 91 octane pump premium fuel that contained 10% ethanol.  I ended up installing a return style fuel system to keep the fuel from sitting in the line to the carb and getting hot, but insulating the fuel line will certainly help.

[rcodecj]

Nowadays fuel boils really easy. Insulate it or move it away from the heat.
I would check fuel pressure when it's hot and cold.

[Drew Pojedinec]

had this problem on my 76 F100.
the headers were like 1/2 an inch from the fuel line!

anyhow, it is insulated now and It is attached to the top/outside of the frame of the driveside tire well.  It runs straight in to the pump.  Never had another problem.
There are plenty of holes to anchor the line to and if ya do it right it isn't really in any sort of danger in an accident (well no more than before at least).

[JimNolan]

When I had a fuel boiling problem in my Mach 1 several years back, I measured the temperature of the float bowl of the carb with one of those infrared thermometers.  I was very  surprised to find that the fuel was boiling when the float bowl was only 165 degrees!  This was with 91 octane pump premium fuel that contained 10% ethanol.  I ended up installing a return style fuel system to keep the fuel from sitting in the line to the carb and getting hot, but insulating the fuel line will certainly help.

   I'm not very smart when it comes to these things but if you leave a pan of gas out in the sunlight in 80-90 degree weather the gas will go somewhere pretty quick. If it didn't vaporize (boil) , where did it go. After my engine in my airplane heat soaked I'd get vapor lock if I didn't turn on the electric fuel pump. In Columbus when I was racing the outside temp was 105, the inside of my engine was 190 degrees but the heat around the fuel lines caused fuel starvation on top end. I don't have that problem in cooler weather. I would probably have been OK if I had open my hood in the staging lanes. Jim

[thatdarncat]

When I swapped a 460 with headers into my '78 Bronco I started having problems. We insulated the line running along the frame rail in the engine compartment with some old heater hose. I also insulated the line from the mechanical fuel pump to the carb with foam pipe insulation ( we figured that would melt near the headers ) Never had a problem again after that. Bronco was a daily driver so looks weren't important, could use something different if that was important.

[ymountainman]

Thanks guys for the responses. I will insuate it and see what happens. Sounds like that will fix it. Thanks!

[Barry_R]

Insulating is you're only choice - unless you go to an electric pump.  Modern fuel is designed around EFI systems and low pressure vapor boil is not considered a critical parameter.  Pressure controls the boil point and a electric system is under pessure - considerable pressure - at all times.  Mechanical pump systems run under vacuum on the feed side, which REDUCES the boiling point...

[Qikbbstang]

Just a note about insulating fuel lines. Be careful that combination of materials you install around the fuel lines to insulate them does that. There is a possibility that metalic covered insulation being double or tripple the diameter of the un-insulated line itself could actually provide more surface area exposed to the heat source which in turn concentrates more heat in to the line. Keep in mind there are two methods of heat the first being ambient - the air temp under the hood and second radiant heat the heat you feel emiting from the source be it from headers, the block etc. 

[ymountainman]

Thanks guys I insulated the lines with armaflex wrap and it fixed the problem completely. Thanks again!

[Ford428CJ]

I agree with Barry on that. You may want to look into a electric pump.... That would be the first choice. Second would be to insulate it but that's not always a cure all. JMHO