Citroen C5 - Changing LDS fluid

[Kees]

Fikse told you the other possible solution to depressurize the system. As i say to Matt Blancs, by this way there keep old LDS in the struts, because the car sit not at the lowest level!!
What you are doing now is 2 different types of fluid mixed. Also you calculate a percentage is no more then a guess!!
If you don't have the tools to do things properly, then stay away from this kind of "do it yourself " should be my advice!!

[fcesur77]

Thanks a lot for your advice! I have a chemistry background and I am aware of the chemical structure behind of two liquids. Both are synthetic hidrocarbon polyalphaolefin hydrolic liquids. Slight difference is coming from the additives, chain lengths and functional groups. That means both fluids have almost the same molecular polarity and tend to dissolve each other perfectly. This will not cause any issue.

[wurlycorner]

Interesting that you’ve noticed a difference in the feel and in the apparent viscosities of the fluid between manufacturers - that should not be the case, if they both conform to the same specs. Could you elaborate a little more on how you determined different viscosity please?
Thanks

[fcesur77]

First observation was visual. I took samples from both oils. Tested the viscosities by Brookfield viscometer in the lab at work. Total LDS is 17 cP, Mannol LDS is 32 cP @ 40 C.

[Kees]

Here you see the results of the Total LDS from a Shell laboratory in the Netherlands between fresh and old LDS from my C5X7 3.0 V6 petrol.

And again the way he thinks it's oke by this procedure is wrong, especially it's not difficult to do it the right way!!

Viscositeit olie
Nieuw bij 20 c
33 cp
Nieuw bij 70 c
9.8 cp

Oud bij 20 c
28 cp
Oud bij 70 c
8.1 cp

[fcesur77]

It is your opinion that the procedure I applied is wrong. Compared to the bottom drain method, I will do the oil change procedure twice. Even if you apply the correct procedure, there will be always roughly 0,5L old fluid in the system. When the hydraulic pump starts to run, it creates pressure and circulation in the suspension cylinders. This will lead to dissolve both fluids each other under pressure. If you do not have knowledge on fluid dynamics do not make comment on kind of technical topics.

[Kees]

You are no more than a stubborn person, Citroën tells how the procedure is the best way, but you say, "no I know better"

[fcesur77]

No worries, I have consulted this procedure to someone experienced in citroen technical service. The only issue is to use more than necessary LDS fluid. Both way is acceptable within the bounds of possibility. Thanks your suggestion though. My suggestion is to you there are alternative ways to do something. It is up to you to evaluate and find out the proper way for you.

[wurlycorner]

Tested the viscosities by Brookfield viscometer in the lab at work. Total LDS is 17 cP, Mannol LDS is 32 cP @ 40 C.

That's quite some difference.
However comparing to these figures...

Oil Viscocity
New at 20 c
33 cp
New at 70 c
9.8 cp

Old at 20 c
28 cp
Old at 70 c
8.1 cp

Suggests something odd with your new Total LDS?
It looks like the Mannol is in the correct range against the previous test results?
Not sure what to make of that.

[fcesur77]

Tested the viscosities by Brookfield viscometer in the lab at work. Total LDS is 17 cP, Mannol LDS is 32 cP @ 40 C.

That's quite some difference.
However comparing to these figures...

Oil Viscocity
New at 20 c
33 cp
New at 70 c
9.8 cp

Old at 20 c
28 cp
Old at 70 c
8.1 cp

Suggests something odd with your new Total LDS?
It looks like the Mannol is in the correct range against the previous test results?
Not sure what to make of that.

No, pay attention to the testing temperature. Viscosity changes based on temperature. It is preferred to measure it @40 C. Because the optimum operation temperature is around this value.

[MattBLancs]

In summary we've data at 20°C and 70°C neither of which can be compared against the data at 40°C. Is the relationship between viscosity in Centistokes (edit: Google has suggested I mean centipoise) and temperature in Celsius a linear relationship?
If so, (with a fresh head as my brain has knocked off for the night!) a quick bit of interpolation in the morning will get a viscosity @ 40°C (from the 20 and 70°C data above).

Attempting not to reignite the heated discussion above, but note it is common in many practical applications that only ever completing a partial fluid change is the best that can be hoped for: engine oil change a significant quantity will typically sit in voids in the head, poorly positioned sump drains, etc. automatic gearbox ATF changes will have the new mixed with a large quantity sat in the torque converter on first use.

Generally, newer oil, of any meaningful quantity is to the benefit of the system.

Further, whatever is put in, so long as meeting the required specification, should work (assuming the spec is correct!)

To be honest, I am quite surprised that a change in viscosity had a detrimental effect on your steering - but equally, I am delighted that new fluid seems to have improved things.

[MattBLancs]

Mannol website, datasheet:

https://www.mannol.de/products/operatin ... -lds-fluid

TDS at the bottom of the page:

PSA S71 2710
DIN 51 524-3
ISO 7308

Hoped there'd be some viscosity data but nowt listed.



Total LDS datasheet:

https://www.online-lubricants.co.uk/pro ... fluide-lds

Specifications:

• PSA S71 2710

TDS

Material Safety Data Sheet:

Viscosity Kinematic (40°C): 17 mm2
/s (ISO 3104).

[PaulC5]

On viscosities, kinematic viscosity centistokes = centipoise / density
so the oil density needs to be known to compare the two but is going to be around 0.8 g/cm3 so cSt will be about 1.25 times higher than cP.

[wurlycorner]

No, pay attention to the testing temperature. Viscosity changes based on temperature. It is preferred to measure it @40 C. Because the optimum operation temperature is around this value.

I'm aware of that.
I was doing a rough quick ratio in my head between the two, probably should have given it more thought and/or put in the data points to draw a graph with an assumed relationship between the two given points and then seen what 40^C fell out at... But ok, I was lazy and did it quickly and may be off - Shoot me for it. Whatever...

automatic gearbox ATF changes will have the new mixed with a large quantity sat in the torque converter on first use.

Yes, doing the fluid change on the ZF box in the mk1 c5 v6 was, painfully laborious and ultimately not satisfying knowing that no how much you've put in, you've achieved a lot of dillution of the crap old stuff, not a proper full change!

[MattBLancs]

Tested the viscosities by Brookfield viscometer in the lab at work. Total LDS is 17 cP, Mannol LDS is 32 cP @ 40 C.

That's quite some difference.
However comparing to these figures...

Oil Viscocity
New at 20 c
33 cp
New at 70 c
9.8 cp

Old at 20 c
28 cp
Old at 70 c
8.1 cp

Suggests something odd with your new Total LDS?
It looks like the Mannol is in the correct range against the previous test results?
Not sure what to make of that.

Simple (linear) interpolation:

New oil
((33-9.8)/(20-70)) = ((23.2)/(-50))
= -0.464
40-20=20
33+(20 x -0.464)=
23.7 @ 40°C

Old oil
((28-8.1)/(20-70)) = ((19.9)/(-50)) = -0.398
40-20=20
28+(20 x -0.398)=
20.04 @ 40°C

Any mistakes included at no extra cost