LHM leak above fuel tank

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LHM leak above fuel tank

Post by szhrr5cc »

My St.Tropez has developed an LHM leak at the rear and, on investigation, this appears to be coming from somewhere above the fuel tank - a stain is clearly visible and drips form from it. I have searched here and found an old post that indicates removing the tank is a long drawn out job not to mention needing an insection pit which I lack. So, I have two questions that perhaps someone can shed light upon;

1, can anyone confirm what is involved in removing a BX fuel tank?

2, does anyone have a diagram of the LHM pipes and system, especially at the rear of the car? I am wondering if the affected pipes can be re-routed to avoid removing the tank (obviously with new lines). I had a leak at the front of the car at the octopus where this idea was successful.

Thanks for any comments

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Re: LHM leak above fuel tank

Post by Jaba »

This is puzzling as there is no LHM line anywhere above the fuel tank. So, do you have any LHM stored under the back seat? Does the leak occur when under pressure or when there is no pressure for example overnight.
LHM is supplied to the rear via the front to rear metal pipes on the LHS sill under the car. It returns (mostly) along the RHS along a similar route.
It is conceivable that one of the high pressure pipes, brakes, suspension or the supply pipes has rusted through and is spraying onto the tank I guess. You could feel along the pipes for any wetness.
These are some of my ideas that might help with your investigations.
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Re: LHM leak above fuel tank

Post by white exec »

If you look in Haynes, there are hydraulic system diagrams showing the approximate position of the hydraulic lines - for both manual- and power-steering models.

Likely that the leak is a plastic fluid return line, from either a rear suspension ram, or the rear height corrector. The rubber elbows/connectors on these lines can perish/split/part company (as you know). For the rear rams, there is a return line, and a vent line (which is simply poked into a drilling in the cross-tube), both coming from the lower edge of the gaiters.

If you're unlucky, the leak could be from a steel high-pressure line, but that could be a sunstantial leak, not the gradual ones seen from return pipework. There's pretty good access to rear end pipework in the area of the cross-tube.
Others here will be able to advise on tank removal - not a job I've experience of. Haynes does have a procedure for it, but hopefully not necessary.
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Re: LHM leak above fuel tank

Post by DLM »

As ever, a picture might help. Are you seeing the leak lhs, rhs or centrally? Is it happening when raising/lowering the suspension?

A common return-system leak comes from a soft plastic three-way push-fit union to the rhs of the car.

It's where the lhs and rhs returns from the rear suspension cylinder gaiters join together with the return line heading octopus-wards. The plastic 3-way rots away over time. Where I''ve seen this happening a leak drip down from the rearward-facing side of the subframe/beam.

Also, where there's a lot of leakback from suspension cylinders into the gaiters, lhm rather than air may be forced back along the gaiter vent tubes and out. I don't think those vents are long enough to spray back over the tank.

Centrally, the only hydraulic component is the height corrector. That's a lot closer to the fuel tank and does have a right-hand bend in the rubber return pipe which is a weak point.

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Re: LHM leak above fuel tank

Post by rutter123 »

Y pieces are nla from citroen.
I believe Chevronics keep them in stock.
Last edited by rutter123 on Tue Jan 11, 2022 9:17 pm, edited 1 time in total.
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Re: LHM leak above fuel tank

Post by white exec »

Y-piece (a Tee) still showing available from Citroen (#16); another similar T-piece is 5270 14, also still available.
and the return piping elbow (#17) available too.
Both for the 3.5mm return piping.
Have very recently laid in a few of the latter.
.
3-way return tee.JPG
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Re: LHM leak above fuel tank

Post by szhrr5cc »

Thanks for the feedback and the various pointers to what may be causing the leak, the diagram is most helpful.

I am currently away from home and will post again, once I have the chance to investigate farther obviously I need to track the leak down and get it fixed, the car runs fine and the suspension is working properly but there is a small pool forming over night.

The car is MOT'd and used regularly; there are various minor issues that I am looking to fix over time, I changed the belts about 18 months ago encountering broken bolts and have been learning more as I go, the BX is a sort of rolling mechanical lesson! As a basic model it is ideal for that purpose. The gearchange suffers from the collapsed plastic part in the linkage that I also need to fix.

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Re: LHM leak above fuel tank

Post by szhrr5cc »

Just remembered I had photos on the laptop
20210925_161844.jpg
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Re: LHM leak above fuel tank

Post by white exec »

That looks like the leak is coming from somewhere in the vicinity of the rear height corrector, and the return-pipes cluster.
Quite an expansive area has been moistened (or crept around), but it doesn't look very wet, which is odd, for a leak that keeps on appearing...
Silly QQ:
Are you sure it's LHM? Is the car diesel or petrol?

Try drying the area off (if actually wet), and placing a clean sheet of board/cardboard under the car, to help pinpoint exactly where it's dripping from, and how much is being lost.
Chris

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Re: LHM leak above fuel tank

Post by szhrr5cc »

The car is petrol 1.4 and it is LHM for sure - experience with other leaks confirms that! I will get the car back on axle stands for a good clean and inspection and measure how much is being lost.

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Re: LHM leak above fuel tank

Post by Fumbler »

Isn't that area where the coiled hardlines for the rear brakes are?

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Re: LHM leak above fuel tank

Post by David »

If the LHM is running down the fuel tank, as it looks in your picture, then I'd suspect the Y connector above the fuel tank.

It's not easy to get to, but not impossible. It's just above the tank, just to the right of the filler pipe,iirc. It joins the returns from the rear suspension cylinders together and then goes to the LHM tank. The return for the height corrector has its own pipe.

Hope that helps.
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Re: LHM leak above fuel tank

Post by szhrr5cc »

Thanks, that may well be it. I shall be having a good look when I am back home

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Re: LHM leak above fuel tank

Post by szhrr5cc »

After a long interval for reasons best left alone I've today been looking at this again as the leak has become noticeably worse. With the car on jack stands I've got under the rear and cleaned any wet areas including the bottom of the fuel tank and then left it for a while to work on something else. The car had been on 'high' as I needed to remove a wheel. The attached photo from the right rear of the car clearly shows LHM originating from the top of the tank at the back (and side, forgot to photo that) which then drains over the surface of the tank to the lowest point and drips on the ground.

Tomorrow I shall have a look at the last suggestion regarding the Y connector above the tank (thanks David). Also, the coiled hardlines for the brakes on this side were wet so that may be a clue also as mentioned previously.

Th suspension goes up and down fine, however, I am now having to top up the LHM tank.
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