Workaround for bubbles in LHM return flow

[xantos]

Well I have tried to rule out o-ring on top of LHM reservoir and connection where the pipe is clamped to the reservoir (see pictures on previous page) with no result... Bubbles are still present...

[aerodynamica]

The basis of the 10 minute mod is that the main return is too far down at the bottom of the filter - and although there are two filters in between, the exit of the main high volume return flow is too close to the intake - it's only about an inch or two at most. In my opinion one mistake Citroen made here is there should have been a flat baffle between the two filters that is most of the width of the tank so that the oil has to pass a long way around the baffle rather than just travelling from one filter directly to the other. A kind of silly mistake in hindsight.

Ah, it was yourself I was thinking of with regard to the original mod a few years ago, Also you're located quite near me as well (usually other Citroen crazies are so far away!) anyway, I think there's truth in what you say about the CX PAS Vs. the Xantia/XM PAS though I did observe that the CX system certainly does return a LOT of LHM to the tank going full lock (not to mention the additional return from the steering column - mounted DIRAVI regualtor) but the return from the CX steering as actually shared with the PRV return and so actually does come back to the tank via the long plastic tube.

When I had the XM mega problems with the bubbles I had clear HP pump tubing and I saw that it was totally clear until I moved the steering whereupon the LHM in the clear tube immediately went white with bubbles (immediately picking up the pubbeles from the PAS as you suggest?) an soon went clear again. A second steering move saw it happen again but this time finer bubbles.

Of course these bubbles when in the pressurised circuit will be compressed to near microscopic size, it's only when they vent to atmosphere they look bad.

Although I have no bubbles in the Xantia LHM now, I don't detect any difference in the ride - it's still like floating on a cloud of diesel But it isn't Hydrative so maybe the bubbles affect the HA in some way. Are you sure the occasional hard ride isn't simply the firm mode cutting in? Not trying to be funny but I always found my HA2 - equipped XM was quite jarring when the firm mode cut in. Similarly on the HA1 of my last XM. I always felt the reaction to the accelerator pedal movement was too sensitive and held on to 'firm' for too many seconds after the pedal was then held still. I listened to the noise of the firmness regulators' coils cutting from soft to hard and back on the LW radio, yes I am that sad

[CitroJim]

Most interesting I never appreciated the bubble breaking role of the filters before!

Did earlier Citroens with a very different design of LHM reservoir suffer this problem, in particular the GS and BX?

Also, does the XM as that (I believe) has a similar reservoir design to the Xantia...

[white exec]

Sounds, Jim, as if XM and Xantia both suffer similar aeration problems, when these occur.
Will do some bench tests on de-bubbling action of the filters in a few days time, when some new filters arrive.

Indeed interesting that this seems not to have been discussed before.
A really informative (and long-running) thread!

No hint in the Citroen literature that the filters had this function. Compare that to the XM coolant expansion tank, which is referred to in the (2.5 DK5) manuals as a "de-aeration chamber" - clear enough.

[lcwin]

Xantos your piping hose is clamp with wrong clamp type . This clamp will distort the hose, change it!
You are taking the LHM directly if the tube goes all the way to the bottom otherwise the suction vacuum created by the Pump will create air intake problems. Go ahead and try what I outlined earlier. You must do the citobic a few times to purge existing air. If you can connect a clear intake hose temporary then you can see how bad is the bubbling.
If there is still bubbles, remove all return pipe ( not the power steering return pipe!) and put it in a container and see if there is any bubble formation.
The most important thing is to isolated the main intake otherwise you will never know what caused the bubbles

[myglaren]

Most interesting I never appreciated the bubble breaking role of the filters before!

Did earlier Citroens with a very different design of LHM reservoir suffer this problem, in particular the GS and BX?

Also, does the XM as that (I believe) has a similar reservoir design to the Xantia...

I was never aware of it in either the GS or BX.

[xantos]

Xantos your piping hose is clamp with wrong clamp type . This clamp will distort the hose, change it!
You are taking the LHM directly if the tube goes all the way to the bottom otherwise the suction vacuum created by the Pump will create air intake problems. Go ahead and try what I outlined earlier. You must do the citobic a few times to purge existing air. If you can connect a clear intake hose temporary then you can see how bad is the bubbling.
If there is still bubbles, remove all return pipe ( not the power steering return pipe!) and put it in a container and see if there is any bubble formation.
The most important thing is to isolated the main intake otherwise you will never know what caused the bubbles

Yes the pipe that goes directlly to reservoir goes to the bottom (almost). On the pics you can see intake filter position and the pipe is positioned on the bottom of filter.
The clamp used on the intake is just there to "blind" the intake, so that LHM doesn't spill through the hole, but I have the same clamp (two of them) where the pipe is connected to HP pump. Might be worth changing the clamp, as the intake pipe inner diameter is 10mm and on HP pump the connection is 9mm...

I did a good amount of citaerobics, but the bubbles are still there...

[lcwin]

xantos use a clear pipe for inlet and check

[white exec]

Have just today taken delivery of a new pair of XM fine-mesh reservoir filters, and put the larger (return) filter on the bench, to check its action in removing bubbles from aerated LHM.

The test was to stand the filter in a clear container, and pour well-shaken LHM into the open end of the filter, and see what emerged. The heavily shaken LHM contained many small bubbles, some larger ones, and a quantity of large-bubble froth.

The LHM that emerged from the filter contained only microscopic bubbles (thousands of them), evenly dispersed, which I guess were small enough to get through the fine nylon mesh. They all appeared to be of the same size order.

All the larger bubbles were retained by the filter, and if the filter was lifted, the level in it took considerable time to fall - falling only as the trapped bubbles and froth dispersed. Nothing of any size escaped the filter.

Then repeated the test using some detergent (producing a great quantity of bubbles), and the result was the same. This time, though, the proportion of bubbles in the poured liquid was much higher, and the last of the liquid - mainly large bubbles and froth - left the filter much slower.

_______

This confirms what several of us have concluded - that one of the principal functions of the filters is bubble (air) removal. Very fine micro-bubbles do remain, and could probably be removed by an even finer filter mesh, but there needs to be a compromise between extreme filtration and adequate fluid flow, especially when the LHM is cold.

It looks as if this bit of the system does do an important job - provided, that is, aeration of the returning fluid is not excessive, and the filters are a snug fit in their mountings.

_______

Having earlier observed a very large number of micro-bubbles in shaken LHM - and which in even tinier form emerge from the filter - I was interested to see whether the LHM in my XM contained tiny bubbles after lengthy driving. Have to report that I've now dipped the tank several times after long and hot drives, and found the fluid completely clear: no bubbles of any kind present. Seems then that the system works well, providing that there isn't massive air ingress anywhere, but that should moderate aeration happen (maybe by copious fluid return, e.g. from steering) the filters will catch it.

Chris

[CitroJim]

This is excellent stuff Good research!

[aerodynamica]

Good stuff!

I think regarding the BX, GS, CX type of LHM tank, that the tank is circular might in some way have the effect of limiting frothing due to retaining low turbulance in the LHM while the vehicle is in motion. I think the XM and Xantia tanks were intended to be shaped to minimise under bonnet space and hence, had a less uniform shape and perhaps the solution to the potential fluid churning caused in the odd-shaped tanks was the extra baffle seen in the XM and Xantia tank.

Good experimentation Wite Exec !

[Mandrake]

Just wanted to report that after 2 weeks the ride improvement from sealing around the pump feed hose has thus far remained.

Here's all I did, just some black silicone sealer around the two likely air leaks - one where the hose clamps onto the tank and also at the join near by. I also put a bit around the top of the mystery o-ring lid for good measure:




The "crashyness" and "bounciness" in the ride that I was seeing a lot of the time is gone, and I did not touch a thing other than applying the sealant. It took about 2 days before I started to notice the crashyness going away in the ride, and after 3-4 days it was gone and has not come back in 2 weeks.

The ride feels more "cushioned" and "refined" now with better damping and body control. Hard to describe it really - previously on undulating surfaces it felt a bit like it was lacking in damping with the car bucking and moving around a lot over some bumps - now it feels a lot more stable and refined. There is still a little bit of suspension clatter over really broken surfaces so I suspect I need to do the droplinks as well, (and possibly the lower balljoint on the right hand side...) but for the first time in a while I'm basically happy with the ride.

Give it a try!

[white exec]

Really good that you've seen that improvement by simply doing those things and nothing else. Would seem to take a while for the air to work its way out of the system, which makes sense.

If a small air ingress in those places is all it takes to compromise the ride, then it might explain why, with age, many cars just seem to lose that magic carpet ride, even though all the other things (spheres etc) have been attended to.

Great result!

[xantos]

That's great! At least someone has some result! I've tried exactly the same thing on my previous TCT Activa with some result... click

Well if you look at my mod I've eliminated the in grease of air with a pipe that is put directly in the reservoir with no effect. Today I've even tried with a diameter 8 (before it was 10) pipe to make a snug fit on the pump connection. A bit better but no dramatic change... But I've noticed that the pump is weeping a bit. Just a bit but maybe enough to suck in air... Oh well still chasing my tail...

[xantos]

This morning after the change of diameter 10 pipe to diameter 8 the steering wheel was hard. I suspected that it might be a bit to small but yesterday it worked fine. Probably because LHM was warm and in the morning the temperature was about 8°C so it was to thick to be adequately sucked into to the system... When I looked into the reservoir it was like a well shaken cola!

Oh well back to square one...