E320 CDI (W210) starting problems,...Fuel shortage?

[CHEWIE]

Hi, New to the "Mercedes Benz Thang" and loving it!
I recently bought a 51 plate 320CDI, which has done 200,000, but is a lovely car well looked after, 1 owner, fsh, etc, although it had had a starting problem just prior to me buying it which "seemed to have been fixed".
In the time I have had the car (3 months) it has now become apparent where the problem lies....The fuel system does not remain "charged" and for some reason the fuel filter housing emptys after a few days with no signs of leaks and this is when I have starting trouble, if I fill the housing with fuel, its starts! and runs ok for a few days (200 miles_ish) but then it starts struggling to start again, so i have to fill housing again.
I assume this should stay full,(or should it?) Maybe it is dropping back? but I dont know why it emptys!
Prior to discovering this I was using Easy Start for a couple of weeks and it would start every time and runs superb and drives fine, plenty of power etc, but the fuel filter housing was still empty! so I can only assume that the fuel is being sucked almost directly across between the inlet and outlet pipes on the top of the housing, so this leads me to think that it is not a blockage in the pipe.
So I wonder is the fuel "pumped" prior to the filter? or is it "sucked" by high pressure pump at front of engine?
I have disconected fuel lines from top of housing (inlet and return) and found nothing comes out with the ignition on, or when cranking the engine.
I had it serviced recently (200,000) Mercedes Approved Repairer, and they couldnt diagnose any particular problem, but quickly told me that if I had further problems they would want it for a week, to run checks order respective parts and then check again over a couple of days, which is all very nice but I dont fancy the bill much!
Anyway hoped one of you guys may be able to shed some light on this for me as Im flumaxed?!
Thanks a lot, Ray.
( p.s when I say empty above, there is about 30mm depth of fuel in bottom of housing, Thanks again.)

 

[Daeths]

check previous threads for what is most likely your problem, i.e leaking fuel pipes or most likely o-rings.

 

[John Kerr]

Sounds like the system is sucking air from somewhere, have you tried a new filter, the fuel has to go through the filter not across the top.The plastic fuel lines to the low pressure pump get hard and can suck air without leaking fuel.

 

[CHEWIE]

Hi, Thanks for that, yes it would seem to point towards the "sucking air thing" as I have heard similar from lots of sources now.
The fuel filter was changed at service (1K ago), I realise the fuel is suposed to pass through filter and not across top, but can only assume that that is what is happening to enable it to run, but not enough to fill housing.
Do you have any idea as to which o rings/fuel pipes I should be looking to replace?
Cheers, Ray.

 

[television]

All of them including the return to tank, that is equally as important

 

[bigtwin]

Just been through this on that engine. After a lot of phaffing and expense - it was indeed the fuel filter. Cheap, simple and obvious - once you have done everything else of course!

Having said that - by 100K the fuel lines were pretty brittle anyway, and a change didn't do any harm.