Leak - Air in diesel system -When Parked

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Leak - Air in diesel system -When Parked

Post by Sloppysod » 13 May 2018, 19:36

Any suggestions where to look first?

If I leave my X7 for about 3 days without using it, the fuel drains back into the tank. Which means I have a leak, however, the leak is not there when the engine is running as I would expect to see diesel everywhere so the fuel pressure must be closing the leak.

Or, does the X7 have a non return valve in the fuel system that could be letting diesel past?

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Re: Leak - Air in diesel system -When Parked

Post by white exec » 13 May 2018, 19:42

Where petrol is normally pumped under light pressure from tank to engine bay, diesel is sucked out of the tank by the injection pump, so a leak of diesel may not show up. Air can be drawn in, but fuel will not leak out when the engine is running.
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Re: Leak - Air in diesel system -When Parked

Post by Mandrake » 13 May 2018, 21:09

Not to mention, air can leak through tiny gaps that liquid with surface tension will not, unless pressurised.
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Re: Leak - Air in diesel system -When Parked

Post by bobins » 13 May 2018, 21:34

I think I'd be looking first at the little push-clip fixings (circled red) for the fuel pipes where they enter the fuel filter. These are the ones where you depress the coloured 'tag' and the pipe spigot then pulls off the filter fitting. They've always looked like a bit of a weak point to me. Check they are attached straight and level and not pulled at an angle.
pipe attach.jpg
Your filter may vary, but the pipe fittings (circled red) will basically be the same.
Also check the filter is fully tightened - the two parts circled blue should be touching which shows the filter has been tightened up properly.
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Re: Leak - Air in diesel system -When Parked

Post by Sloppysod » 14 May 2018, 20:16

Cheers, Guys,
Probably the connectors circled in red, they seemed very loose the last time I changed the filter so I put a tie wraps around them to make sure the white bits did not fall out !!
Ouch!....New pipe (filter to Pump) = £36, New Filter Housing £90
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Re: Leak - Air in diesel system -When Parked

Post by Gibbo2286 » 15 May 2018, 09:11

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Re: Leak - Air in diesel system -When Parked

Post by white exec » 15 May 2018, 09:16

That will stop fuel draining back into the tank, but won't stop air getting in.
Most diesel fuel filters have a non-return (one-way) valve built into them already; iirc, Purflux has two.
Air-in-fuel needs to be sorted.
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Re: Leak - Air in diesel system -When Parked

Post by Gibbo2286 » 15 May 2018, 10:30

white exec wrote:
15 May 2018, 09:16
That will stop fuel draining back into the tank, but won't stop air getting in.
Most diesel fuel filters have a non-return (one-way) valve built into them already; iirc, Purflux has two.
Air-in-fuel needs to be sorted.


But they do fail and the add in valve is the cheapest way to fix it, I'm not sure the op has air in the fuel or it's just drained back and he 'thinks' it has.
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Re: Leak - Air in diesel system -When Parked

Post by white exec » 15 May 2018, 11:15

Unless there's air ingress (even at the pump, or maybe further back), fuel won't be able to drain back, surely? - pipette action.
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Re: Leak - Air in diesel system -When Parked

Post by Sloppysod » 15 May 2018, 21:49

Bought a new filter house top which will cure one end including the syphoning back, next will be a fuel feed pipe (1579PV) unless I can get just a connector - any ideas?
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