O-rings CAN allow air to enter with no fuel leak being present.

The o-ring at the pre-filter is a separate part number from the pre-filter and is missed very often. The pre-filter itself with its clip type extension washer/holdown can be difficult to make seal sometimes.

The only line that should drain at shut down is the line from the pre-filter back to the fuel theromstat mounted in the cyl head. It will drain back ~3/4's the length of the line. It is a short (3" or 4" line) mounted on the top left of the fuel filter housing.

You should not see bubbles in any of the lines connecting to the shutoff valve when running. If yu do there remains a samll leak somewhere.

__________________
Terry Allison
N. Calif. & Boca Chica, Panama

09' E320 Bluetec 77k (USA)
09' Hyundai Santa Fe Diesel 48k (S.A.)