Paccar fuel filter doesn't stay full

[Rawze]

Have you pressurized the fuel tanks to 10 psi and let it sit a few hours to check for leaks?

I have also seen cracked welds at the top of the pick-up tubes inside the fuel tanks on a few trucks that allow air in too. Putting a fuel line into the bottom of a bucket and using air pressure to push the fuel out of the tank will show bubbles mixed with the fuel to reveal this.

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If it were here, would be interesting to see for myself the difference in micron ratings and to help find a possible cause.