Good to hear you have been changing the secondary fuel filter every six months on your 240d. If you install a pressure gauge to monitor the pressure in the base of the injection pump. It will tell you when the filter should be changed.

The total cost of this is approxamatly two secondary filters. So basically it is free if not saving money as well. There are several other benifits as well in having that gauge installed.

Also benifits to reduce the amount of filter changes by simply replacing the piston pressure spring in the lift pump with one from any junk 617 or five cylinders lift pump. This elevates the pressure out put of the 616s lift pump.

This way it can deal with filter restrictions much better delaying further the change intervals required of the secondary filter. You may find if the fuel is clean in your area that a filter may only be required every few years for example. Or if you pick up a load of really dirty fuel you need it now.

For many reasons you especially always want decent fuel pressure in the base of the 240ds injection pump. This is not expensive to have and monitor. Low pressure may result in paying a price you do not want to pay over time.

Those that only change fuel filters in 240ds when they are totally restricted or performance has droped off may pay too high of a price in my opinion. Plus without the gauge they either are not really sure why performance has dropped or are unaware it is substandard to start with.