Installing pre filter to 3l CRD

Hi all, I have just joined the forum so still finding my way round so thought I should ask a question about my current job.
I am trying to install a pre filter at the rear of my ute near the main tank but I dont know which line is the main feed to the engine, there is a larger 10mm & smaller 8mm line neither of which is pressured when disconnected with the ignition on so I am now not sure which is feed & which is return.
Question is can anyone tell me which one goes to the main filter then onto the fuel rail & which is the return line.

Thanks,
GTB
By the way this is a great forum thanks to all those who participate...

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Originally Posted by got the bug

Hi all, I have just joined the forum so still finding my way round so thought I should ask a question about my current job.
I am trying to install a pre filter at the rear of my ute near the main tank but I dont know which line is the main feed to the engine, there is a larger & smaller line neither of which is pressured when disconnected with the ignition on so I am now not sure.
Question is can anyone tell me which one goes to the main filter then onto the fuel rail & which is the return line.

Thanks,
GTB
By the way this is a great forum thanks to all those who participate...

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I'm sure someone will be along to help Mark, I've given it a bump for ya.
Cheers, the ferret.

Usually the larger one will be your feed, Just have it running and pull the lines at the tank one will suck and one will flow fuel back to tank or you could put some diesel in a container so she dont run out fuel on you put the 2 hoses in there and see which one is doing what. As i said though the larger will normally be the feed.

Thanks The Ferret & Nissannewby, I have hooked up to the 10mm line as suggested & all seems fine now. Nissannewby, I tried your idea with the hoses in a bucket & started the motor but even running at 2500rpm the suction & return hoses didnt seem to be either sucking or venting & I had thought these common rail motors needed large quanities of fuel thru the injector pump to cool it , maybe not ey. Anyway it primed up nicely & seems to run fine so thanks for your help.

GTB