Citroen XM Forum

Dieselman wrote:There appears to be no vent pipe, unlike previous LHM tanks.

Surely, all it needs is a vented cap with a pipe that loops back under the tank.

This issue is exactly tthe same as 2.5TD coolant header tanks rupturing.

Wow.

I wonder would a mod to the cap to make it like the XM one with a drain pipe etc, be in order, or would this not be feasible given what KingP has said...

Ciarán

Wow indeed.
While collecting some parts, I casually mentioned the issue to our Cit main dealer workshop here, and it was obvious the chief mechanic didn't want to talk about it, but just walked away. Most odd.
Apparently for some years there was no warning to owners about the need to remove cap before jacking.

To be fair, most mechanics walk away from me when I mention Citroen XM....

This was concerning C5/C6 though. Several of the former in the workshops at the time.

Chris, is this just X7 C5's or all C5's?

Russ, the thread relates to C5 MkII - http://www.frenchcarforum.co.uk/forum/v ... 8&start=15

Good lord. Well I expect that's X7 model then. All a bit scary.

No-one seems to have come up with a definitive reason for the (originally) sealed reservoir cap.

Suggestions have included:
- anti-spill in case of roll-over
- prevention of moisture ingress (although suggested that LDS is no more hygroscopic than LHM)
- necessity of priming the hydraulic pump with gentle reservoir pressure

Apparently there is now Citroen advice to owners to make reservoir topping/filling/fluid renewal a Cit workshop task, where use of a Facom tool pressurises the reservoir to 0.5 bar.

There is advice, now, on jacking and MoT/workshop procedures with regard to body lifting.

Appears that the reservoir cap has been revised by Cit to include some kind of pressure valve, possible a one-way device.
No-one on FCF seems to have tested one of these newer caps definitively.

Split tanks are reported with some regularity.

Not sure quite how many later Cit models are prone. Seems like C5 and C6. EDIT: See post below.

The above is only to the best of my understanding.

FCF contains some interesting posts, but depth of technical knowledge (with the notable exception of a few individuals) and reference to Cit technical literature and repair procedures seems a bit thin. May be lots of reasons for this, including the unavailability of reference material. We are well served here vis-a-vis XM, I think.

russ92xmsed wrote:Good lord. Well I expect that's X7 model then. All a bit scary.

Russ,
X7 = C5III

Done a bit of cross-checking on parts though:

Hydraulic reservoir, 4009 S4
Used on C5, C5II, C5X7 (=C5III), C6

Reservoir cap
Original type, 4009 H6 - used only on C5
Later type, 4009 L6, which has been superseded by 4009 V9 - used on C5II, C5X7, C6

A lot of hydraulic systems have a sealed resovoir mainly to prevent contamination of the oil but there are other reasons for this setup.
The XM and earlier citroens used a 'built to leak' system that requires the resovoir to be at atmospheric pressure to allow the return pipework to operate and so had to be open vented, LHM was p[robably chosen as a result of this problem, make no mistake, there are many reasons an open vented hydraulic system is a bad idea.

The advent of the electric pump means that there is no needless circulation of fluid but i believe the return system on later citroens is not a simple catch and return setup therefore the resovoir could be sealed to prevent contamination of the LDS fluid which i am lead to believe is hygroscopic but offers a much better performance under extreems of heat and pressure. The sealed tank also ends the age old issues of air locked pumps and undetected air ingress to the system causing all sorts of operational issues.

The problem as i see it here is that the tanks should be welded stainless steel construction, plastic tanks do fail like this in cooling and hydraulic systems but are lighter, cheaper and do not risk contaminatoion of the fluid through corrosion which could lead to catastrophic failures within the hydraulic system like a plain steel tank could.

Citroen did later fit a pressure relief cap to counter the problem although this will not completely solve the problem, the fact is the cap should be removed before fully depressurising the system and many of those that have failed have done so because the manufacturers instructions were not followed.

D