Casey suggested:
"a mechanic friend of mine told me if I couldn't find the right
vented cap for the POJ, to buy a normal one and remove the rubber gasket, the
brass spring plate will still work, but will not completely seal out the air,
if you don't like that, cut 2 small grooves in the rubber creating a channel
on the seal so as to not get a vaccume..."
My concern with this is sloshing. With the tiny tanks most of our
cars & trucks are saddled with, many of us (including me) FILL them right up
to the brim. We want every last oz. of capacity we can get. The factory caps
allowed pressure to vent, but kept the gas from sloshing out all over the
outside of the truck and the road. The modern sealed ones may well be
dangerous.
Imagine a hot summer day. The truck is sitting in the sun and the
tank is half full. The heat expands the air and gasoline in the tank causing
a positive pressure. As the pressure builds it "searches out" weak spots in
the fuel system trying to equalize with the outside pressure. As the pressure
builds it stresses all the rubber parts of the system and even the tank
itself. Eventually something will have to give. The final failure of the fuel
system could be catastrophic, allowing the internal pressure to vent rapidly
in a gush of hot fuel vapor. There are few things on earth more explosive
that hot gasoline vapor.
What we have created is basically a bomb. All that is needed to
insure your friends read about you in the newspaper is a spark, maybe from
your buddies stinky ole stogie, maybe from a grinder or welder, or maybe even
from just static electricity. If your driving the truck, you will be actually
sitting on this bomb.
The opposite can also happen. Imagine a cold winter day. You are
climbing a long steep hill with the ole stovebolt roaring away WFO drawing
fuel as fast as it can carburate it. Once again the system is sealed. Now we
can develop a LOW pressure problem. You might see fuel feed problems
resembling vapor lock or if the fuel pump is really strong, the tank could be
collapsed possibly allowing a gas leak - once again right in your nice cozy
little cab.
The engineers that designed these fuel systems were not fools. Modern
cars have sealed systems for emission control reasons and are designed with
internal vents. Sealed caps are a necessary part of those systems. Bob
ADler's suggestion: "I've been using Stant G23. Local parts stores have
them. they are vented but seal when rolled over, as in an accident. Best of
both worlds." would seem to be the perfect solution. Thanks Bob, I'll get one
on order.
Paul O'Neil,
1951 Chevrolet 3600 Pickup Project, See it at:
The Poor Man's Advanced Design Tech Tips Page
http://home.earthlink.net/~conntest47/
Fullerton, California USA
Hudson29@aol.com
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