Join Date: Mar 2001
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Our tank vent is lower than the deck fill, so excess fuel will come out of the vent before the splash back will automatically shut off the pump. Even if the vent was in sight while filling, I'd hate to wait until I overflow to stop filling. I know my capacity, but my usage is an estimate at best, an estimate that I refine as I go by filling the tank to capacity each time I fill it. I also feel more comfortable with my estimate of how much fuel remains (and therefore how much is needed) if the starting point is a full tank, rather than some guesstimate.
The whistle is supposed to make a very loud, shrill sound while filling until the fuel level blocks the vent hose, at which point it stops. It seems like an easy, inexpensive thing to do to avoid spills. And nary a magnet, nor other dubious science, in sight!