Has anyone ever come across info on the boiling temp of today's gas related to pressure? When my car's hot, the fuel seems to be boiling in the fuel line resulting in very little fuel visible in the clear fuel filter. The suction side of my fuel line runs near the exhaust manifold. Wondering whether an electric pump would fix it - the fuel in the line would be a 6 psi instead of negative pressure.

The boiling point should raise 1 degree C per 1 pka irrespective of atmospheric pka. With the boiling point being 100C at 1 pka(atmospheric) There is not not much to gain with an expected 2 or 3 pka difference between a properly working mechanical pump and a well adjusted electric pump. :rolleyes: You would quickly run up against the limitations of your float switch before you would defeat the boiling. Better to just keep the fuel cool.

Bob, You would be much further ahead by putting a return line back to your tank. The fuel will stay a lot cooler because it doesn't stay near the headers for a long enough time to get hot.

Jim G. 67 conv 400

Not sure what you're talking about, Jim (Fbody69). My mind works in degF and PSI. I can't believe gas boils at 212F at 0 psi (gage). It has to be a lot lower. I've felt the fuel line and it's not too hot to touch (maybe 150F?) There would be a 6+ psi difference in the fuel line where it passes the manifold, the difference between the suction side of the mechanical pump only and pressurized to 6psi by my Holly Red pump in the back. Jim G., that makes sense. Maybe a future project. I'd have to replace the sender unit with one with a return line.

Basically, you would just raise the boiling point a few degrees by adding pressure.
You probably have a weak mechanical pump.

If you are saying you have an electric pump and a mechanical pump working in series, that would be a problem. They need to be run in tandom. They need to be T-ed before the mechanical and then T-ed again before the carb. Running the two like this works great! I run them that way for using Nitrous Oxide. When using NO2 a lack of gas is a detenation. Can you say, "There goes my carb, it's a UFO"!

Bob,

I don't think your problem is the gas. Underhood temperatures have been rising over the years and newer fuels contain additives to keep the fuel stable at higher temperatures.

Hey Hammered, the difference is that today's fuel injected cars have high pressure fuel lines and are pumped from the fuel tank. I was suspecting that our cars with the pump on the motor with the fuel line at less than atmospheric pressure may have problems. I googled "gasoline boiling point" and determined that the answer does not exist and that gasoline is a chemical engineering nightmare.

Here's everything you ever wanted to know about gasoline:

http://www.faqs.org/faqs/autos/gasoline-faq/part1/

Seems to me, Bob, that if this was a widespread problem, we all would be boiling our gas away. Don't you think it could be something about your car in particular? I'm sure your weather is a lot like my weather. My car is black and HOT! And I'm sun burnt and smilin' today!

Maybe without a clear fuel filter you have no idea that the pump is pumping mostly gas vapour. My car still runs - there must be enough liquid fuel spitting through to keep the bowls full. I had an electric pump in the back but I removed it because it was in the way of the transverse muffler I installed. I'm considering reinstalling it.

My car more than just runs! I'm sure it's going through a gal a minute at times and I have a stock mechanical pump. Diaphrams go bad often and will pump, but will pump weakly and not be able to make pressure. Especially on car that sets a lot. If you don't have 4 pounds of pressure in your supply line theres a problem with the pump.

I've got a gauge in the line that shows 6-7 psi. I'm talking about the suction side of the pump which would be less than atmosphere.

Would not matter because once it got to the pressurized side it would go back to the liquid form.
It's possible your pump is sucking up air somewhere between the pump and tank. That would make it look like you had vapor in the line when it is really just air. Could be that clear filter is letting in air.

Other than not seeing a full fuel filter, what problem is the car having? It's not uncommon for the filter to be less than full. Is it running okay? If so, there isn't a problem.