You may be right of course. But some people do the purge and the fluid in the container that is returned remains pretty clean.

On the law of averages the secondary and to me the most important filter is not changed out frequently enough. There has been a tendency to leave them in service perhaps for longer than they should be.

Some believe that even until the engine shows signs of fuel starvation. It is a false economy to do so. Too many reports have appeared over the years. Basically claiming their fuel milage increased after they changed the filter on these engines. Logic would seem to apply that a starving engine would burn less fuel. Also since they were not looking for this it would have had to be at least a mile or two better fuel milage per gallon for them to have even noticed it.


The archiles heel is as the filter becomes more obstructive as time goes on. It reduces the available fuel pressure in the base of the injection pump. So operationally speaking chances are it is cheaper to change the fuel filter periodically than almost never. And remember it is the only water trap you have unless you install an aftermarket one.


Also as the filter starts to present a greater pressure drop or resistance . The chances increase of forcing more dirt through the element. Based on the pressure differential is increasing.


Personally I like spending money where the benefit is greater than not doing so.