Ok so what is the workings of a fuel tank. How does the vent work, i understand to keep air pressure equal inside but during fill -up what cant fuel escape out the vent? Is it actually mounted higher than the opening of the filler tube? Mainly I'm asking since I'm getting an old 50 gal semi tank to use as an aux tank. Its aged looking. I might need to replace the valve on the bottom, but it has what appears to be a vent valve on the top. Like you can either have it vented or not. I need to look more id depth at it though, but it is mounted higher than the filler. I know our fuel tank caps are one way vents but what about some of these after market tanks. Vented or not? or both? I hear about home made tanks, what type are they? Thx - a very Bob

 

Usually the vent is on the top to let air escape as you fill the tank.

 

Hoss built his tank out of concrete to match his bedliner. Listen to him - - he knows.

 

Now Bob...why would I go to the trouble of BUILDING such a thing when they are so readily available.

 

Usually, the average vehicle tank has a vent tube in the highest place in the tank which routes back to the filler neck near the end. This is to allow the filler neck to accept fuel without gurgling all the time. I remember a ford mustang which had been hit in the rearend and had the vent tube pinched. It was a real PITA to fill but since it belonged to the boss at the station I worked at I had no choice.

For emissions the tank is nowadays sealed with the cap and a vent goes to a cannister under the hood to keep vapors from getting out to the air. The vapors get sucked into the engine vacuum on a gasser. I don't know how they do it on a diesel. My 1st gen doesn't have a cannister that I can find.

Edwin

 

Love it, Hoss. Great. Matches the liner perfect.