The 08' 3.0 X5 has been having this problem since new, right off the dealer lot.

I fill up the gas tank till the pump clicks. I start the car and see the gauge a bar less than full (a small bar). So I get out and pump again, click after click, about one and a half gallon more goes in. I go back and start the car again and see the bar at full.

That's the ritual I go though at every gas station. The car went in for service but the tech told me to fill up the car slower so gaseous air would have time to ventilate. In short, don't use the pump at full power. The tech didn't have permanent fix for it and I didn't push it.

The car's still under warranty but I think it's not a big deal so I'm willing to just let this one go. But will it have a negative impact on performance? The pressure in the gas tank might be off due to faulty ventilation. Or is it? I'm not sure in the long run if this will haunt me back as a performance lag or lower reliability. Or if it's just a small annoyance which has no other ill effects. Any help is greatly appreciated.