Filler Neck Question

[tucsonjwt]

I see some squares (like my 83 C20) have just a short hose that goes directly from the short filler neck into the gas tank, and other squares have two long extension tubes that go from the filler neck to the tank and then connect with two more hoses. What are the long extension tubes for - 16 gallon tank?

See pic.

[xrcr]

I think you are right. I put an 83 bed on my 76 chassis with a 20 gal and I had to really shorten the filler. Somebody smarter than me should verify.

[tucsonjwt]

This filler neck came out of an 81 C10. I don't know if this was unique to 81?

[tucsonjwt]

Does anybody have a 16 gallon tank truck and does it have a filler neck with these long extension tubes?

[Security guy]

I've got a short Silverado with dual 16 gallon tanks. Both sides have the tubes just like pictured above. The small hose attaches to the filler neck. I'm guessing its either a air vent for when your pumping gas, allowing air to escape as gas goes in, or its an anti-siphoning vent...

[tucsonjwt]

Thanks. Mystery solved. Long extension tubes accommodate the shorter length of the 16 gallon tank.