Given the intelligence evident on the list (we all choose to drive an LBC
after all), it surprises me to see the wasted bandwidth on a discussion
about why a fuel filter isn't completely full. If you use your noodle for a
second before you return to typing, the reason is obvious. At least it was
obvious to the students in my wife's third grade science class. She held up
a fuel filter horizontally and explained that liquid enters on one side and
exits on the other. Starting with an empty filter, how high will the liquid
rise before it exits the other side and how much air will be left inside?
OK class, repeat after me, "The liquid will rise to the level of the top of
the exit opening". Therefore, the level of fuel in your filter is dependant
upon the orientation of the filter exit opening. If a bubble bothers you,
or you want to make full use of the fuel filter surface, orient your filter
with the exit opening on top.
Now to the original question which started this mess. The poster indicated
that he had filled his filter using a syringe and that the filter later was
only half full. The horizontal filter represents a high point (no, not THE
high point. Any time you have an apex in a liquid handling system it is a
high point) and gases can potentialy accumulate therein. OK, so what kind
of gas? We assume that due to the volatility of gasoline (petrol) and the
lack of pressure when the system is off, that there will be some evolution
of gas. Upon starting the fuel system, the resultant bubbles will travel
along quite nicely until they reach a high point, and then they stay there
because they can't be displaced. It really doesn't matter what kind of gas.
I suggested that the lister pull a vacuum on his system because it could be
breathable gas getting in through the suction side of the pump. Just
because a system doesn't leak under static conditions doesn't mean it won't
leak under pressure or vaccum.
To be fair...
A few of the third graders incorrectly responded that the filter would fill
completely, so you guys aren't all alone in this assumption.
Lonn Howard
'70 TR6 -mine
'71 TR6 -in my garage, therefore it's mine (dad might disagree)
'70 MGB GT -mine, mine... all mine
'89 Saab Turbo Convertible -hers
"We are but temporary custodians with an obligation of preservation."
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