HardRockNM
Well-Known Member
If your filters are losing prime you will either have a blockage or you are sucking in air somewhere. It sounds like you have eliminated a blockage so that leaves sucking in air. Whichever filter that is losing prime the air leak will be in the line before the filter that loses prime. I would carefully check your lines and every place they make a connection. It is possible to have a leak in the suction side of the fuel system and not have fuel leaking.
One of the mines I work at has a CAT 980G with this problem; it's got a pinhole letting air in, so needs to be primed at the beginning of the day and whenever the machine is shut down for more than around five minutes. The dealership mechanics can't find the leak, so they just deal with it.