Sight tube rule

[Jersey Tom]

For the life of me I can't figure out a good reason for the sight tube not being allowed lower than the top plane of the fuel tank. Anyone? Seems like it would make the sight tube a lot more functional and lead to less "oh shit that filled fast!" spillage.

[Jersey Tom]

For the life of me I can't figure out a good reason for the sight tube not being allowed lower than the top plane of the fuel tank. Anyone? Seems like it would make the sight tube a lot more functional and lead to less "oh shit that filled fast!" spillage.

[enginemike]

If the sight tube comes off and it's mounted to the main body of he tank you will have a big mess on your hands. on the neck there's less of an issue I guess.

[js10coastr]

I forget where I read it... and no guarentees that I get the story right.

But there was some sort of racecar that had a filler neck below the top of the tank. When the tank was filled up ther was a pocket of air stuck at the top of the tank. As the race went on, the air pocket heated up, and being air, expanded and pushed the fuel back up out of the tank... spilling fuel everywhere.

[Tony K]

Right, I can see why you wouldn't want the filler neck below the top of the tank without a real nice vent line because that's just asking for trouble.

I would have to agree that having a useful visual fuel gauge would be uber-nice, and can only think that the issue of the sight tube becoming disconnected or damaged would be the main concern. We have a clear (well, yellowed now) PVC filler neck extension which helps with overfilling, but it's not very useful for a fuel gauge.

[Buckingham]

ebay item #: 120049247908 http://fsae.com/groupee_common/emoticons/icon_smile.gif

[Biggy72]

The only reason I could think of for the sight tube to be in the filler neck is so that the mark the officials put on the tube is very accurate. If the tube is on a lower part of the tank a slight tilt of the car could put quite a bit more or less fuel in the tank and it would be harder to have the exact same amount in the tank every time.

[Will_K]

Consider the definition of volume as you might see it in calculus, the integral of surface area with respect to distance. In this case, when your gas tank is being filled, they want to get it as precisely at a known volume as possible. The only control they have is the height of the top of the fuel.

So, having the sight tube in the filler neck, which has smaller cross sectional area, is more precise... +/- 1 mm in the filler tube is a smaller variation in volume than +/- 1 mm in the tank.

[Preston Schipper]

I think he meant have the site tube start down low. It always sucks to be filling the tank, wait to see the fuel in the site tube on the filler neck, then all of a sudden the fuel shows in the site tube and its too late, fuel spills everywhere. It'd be nice to have it start low as a working reference as you fill the tank.