Hey all. Ive got a 66 galaxie that just became road worthy. Drove aruond for a while tonite and when I got home I opened the vented gas cap to hear voooop!. I seems that it builds pressure not vaccum in the tank. The gas cap ive got only allows air in not out. Any coments? Matt

That's what it is supposed to do. Vented caps only vent in one direction...in. This allows the the pump to draw fuel from the tank without trying to collapse it.

We had '66-LTD in the shop for complaints of dying at idle, no power @ times and extremely lean idle condition. The fuel starvation was so strong at idle that the fuel level in the 4100 would drop low enough and car would die after a 10 to 15 minute idle period and hard throttle uphill would produce a lack of power, cough, sputter and dying. We first drilled a 1/8th sized hole in cap @ went for road test; problem solved. The cap was a non-vented type but there were no identifiers on it.He also heard "whushing/whomp" sound too, when removing the cap, because the pump was creating an in-tank vacuum condition. He'd already paid for tank R&R, cleaning, and a strainer replacment elsewhere without any improvement in condition. JME