Re: Vapor lock

[jlandry@domain.elided (John A. Landry)]

In a brilliant stroke of genius, Chris & Ranae Procyk <procyk19@domain.elided>
blurted out:

>So what really *is* vapor lock?

My understanding is that the term refers to a situation where fuel turns
from a liquid state to a gaseous state due to the application of heat.  The
word "lock" might be a bit misleading I guess in modern times.  Could it be
in the "old-days" a fuel pump might actually need to be re-primed if a
vapor bubble halted fuel delivery?

>I mean, I know that our mechanical fuel pumps are "self-priming"-- which means that they can pump air-- so why can't they deal with fuel vaporization??

In a severe case, if enough fuel is being turned to vapor, then even if a
fuel pump is self-priming, all it will be pumping is vapor!  Liquid fuel
would not be supplied to the carburetor.  The problem is typically more
pronounced at idle and low vehicle / engine speeds, because the volume of
fuel required by the engine is small and therefore the volume being pumped
is small.  The slow flow of fuel in a fuel line gives it more potential
exposure to heat.  If a vapor is created in the line by the heat exposure,
then this vapor will be pumped into the carburetor resulting in fuel
starvation.

I've experienced "vapor-lock" at low operating speeds before, but never to
my knowledge at highway speeds.  I suppose this is possible if the fuel
line got *really* hot when routed next to an exhaust manifold or tube.

My $0.02...

John L.
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