LHM use by?

basil · Unread post by **basil** » 07 Jul 2006, 20:16

Hi, I found some LHM fluid in my shed which is@8 years old ,is it safe to use

Thanks
________
BMW R100S

Unread post by **alan s** » 07 Jul 2006, 20:44

If it's been kept in a sealed container I can't see why not.
This has been discussed before and the concensus was it should nearly last indefintely if kept from the elements.
Only thing to check is that it is LHM+ and not the old type LHM which I am led to believe is a bit thicker and can cause later model cars (Xantia and XM) to get a bit stiff in the ride. If it is the standard stuff, you may find a D or CX owner that would gladly swap you for an equal amount of LHM+ as they usually prefer the standard stuff.

Alan S

Mandrake · Unread post by **Mandrake** » 07 Jul 2006, 23:20

alan s wrote:If it's been kept in a sealed container I can't see why not.
This has been discussed before and the concensus was it should nearly last indefintely if kept from the elements.
Only thing to check is that it is LHM+ and not the old type LHM which I am led to believe is a bit thicker and can cause later model cars (Xantia and XM) to get a bit stiff in the ride. If it is the standard stuff, you may find a D or CX owner that would gladly swap you for an equal amount of LHM+ as they usually prefer the standard stuff.

Hmm,

So LHM+ has significantly lower viscosity than LHM ?

Interesting....got any figures ?

Reducing the viscocity of the oil would have quite a big effect on the calibration of the damping valves - you would get less damping....so a car that was critically damped with LHM could be underdamped with LHM+

Regards,
Simon

AndersDK · Unread post by **AndersDK** » 07 Jul 2006, 23:43

Thats not exactly true Simon -

We are not talking like engine oil differences from synthetic 5W40 to mineral 15W40.
The main property of the LHM oil is not its specific viscosity - but its viscosity stability over temperature.
Out of memory the LHM oil has a boiling point of some +250degC - and a pourpoint of some -55degC. The LHMplus extremes are quite close to these figures - just marginally "better".

As for the sphere damper valve - only the center bore orifice would have any influence on the LHM viscosity - and then only at very cold temperatures as we then approaches the pour point.
The damper's center bore orifice sets the "low-speed" stability of the suspension excursions. In effect you will then have MORE stability at cold temperatures.

As for the shocker valves - those springsteel shims calibrated for the sphere location on car/axle - there will be no effect. Because a fluid moving with a high amplitude of acceleration still acts as solid material against the spring - as long as it is a fluid.

No - the difference is only interesting for old model owners - as a "wannabe" to get as close as possible to original fitted parts - and materials. The true addiction.

Mandrake · Unread post by **Mandrake** » 08 Jul 2006, 02:39

AndersDK wrote:Thats not exactly true Simon -

We are not talking like engine oil differences from synthetic 5W40 to mineral 15W40.
The main property of the LHM oil is not its specific viscosity - but its viscosity stability over temperature.
Out of memory the LHM oil has a boiling point of some +250degC - and a pourpoint of some -55degC. The LHMplus extremes are quite close to these figures - just marginally "better".

Well since alan gave no viscocity figures I was just speculating...

As for the sphere damper valve - only the center bore orifice would have any influence on the LHM viscosity - and then only at very cold temperatures as we then approaches the pour point.

The damper's center bore orifice sets the "low-speed" stability of the suspension excursions. In effect you will then have MORE stability at cold temperatures.

I wasn't talking about temperature related changes I was talking about the implications of a different viscocity at the SAME temperature and what effect that would have on the damping. Naturally there will be some variation with temperature, but it will be small.

As for the shocker valves - those springsteel shims calibrated for the sphere location on car/axle - there will be no effect. Because a fluid moving with a high amplitude of acceleration still acts as solid material against the spring - as long as it is a fluid.

You're right about the shim opening calibration not being affected by the oil viscocity - it will take the same amount of pressure differential (impact force) to open the shims as before, however what you've missed is that once the shims do open the oil viscocity plays a role in how much energy is absorbed by the oil flow through the holes under the shims.

At the end of the day a hydraulic damper absorbs energy by converting the oil flow kinetic energy into heat energy through viscous losses caused by the turbulence generated by the oil flowing through small restrictive holes at high velocity, something which oil viscocity affects.

It's likely that the difference may be small however, I wouldn't think that they would change the forumlation of LHM to such an extent that existing systems would be compromised...

Regards,
Simon

Unread post by **alan s** » 08 Jul 2006, 04:23

The whole thing is speculative, as to my knowledge I can't remember Citroen ever making any public announcements about why or when they changed from LHM to LHM+, I also can't say I've ever heard anyone quote a viscosity figure for either fluid.
I was told in the late 80s that Citroen had entered 3 or 4 "experimental" BXs in rally and they were filling all the major placings when they started having catastrophic hydraulic failures with one car apparently having the hydraulics blow to such an extent that the fluid ignited on the red hot exhaust and burnt the car out (Shades of Colin Mc Rae) and it was rumoured at the time that these cars were fitted with a suspension that adjusted itself to road conditions (hydractive???)

The first hydractive car produced commercially by Citroen wasn't until the XM. Coincidentally, if you look at the owners handbook for a later model BX, (mine is an '89 DOM) you will see they then recommend the LHM+ so it would be a fair bet that possibly the problems they had with the BX rally car with the obviously prototype hydractive showed them that the standard LHM wasn't up to the job and the + variety was developed to overcome these problems; but again, pure unfounded speculation.
Owners of CXs and Ds were and some still are sceptical about using the LHM+ in older models, now it could be the liquidity, it may be that it contains more lubricating properties, as I say we are speculating without facts at fingertips, but they are of the opinion that it can cause a small leak to grow which is why I suggested checking and if it is the LHM standard version, it would be of interest to these people.
Not too many years ago, I was topld there was a company in Scotland who was still blending LHM so if the poster is from that area, there is a chance it could be the old stuff.
We could still buy it out here from BP up until about 3/4 years ago, after which they went to LHM+ after I boned them out for hitting us with a 110% price increase without warning or justification and accessed LHM+ from an Independent Total dealer for less than their LHM was prior to the price hike.

Alan S

P.S. With your obsession on Citroen hydraulics, you might like to have a read of this if you haven'
t already found it.

http://www.citroenet.org.uk/miscellaneo ... ics-2.html

Mandrake · Unread post by **Mandrake** » 08 Jul 2006, 10:17

alan s wrote:P.S. With your obsession on Citroen hydraulics, you might like to have a read of this if you haven'
t already found it.

http://www.citroenet.org.uk/miscellaneo ... ics-2.html

Hi Alan,

Thanks for the comments. Yes I've found/read that link before, in fact I printed out a copy of that article of the anti-roll DS's for my father

Fascinating that they did it so long ago. Essentially the system is probably similar to the Activa but minus the computer. (obviously)

When you consider that the actual anti-roll part of an Activa is purely mechanical/hydraulic its easy to see that such a system would be possible, after a fashion, even in the 50's/60's.

The problems they probably ran into (apart from the obvious one of increased complexity) is exactly what the computer in the Activa solves - knowing when to enable and disable the anti-roll function -

Enabling and disabling of the "activa sphere" connected to the rams based on speed and steering wheel input etc, something which would be near impossible to measure/calculate without a computer. (Although a simplified version of it might have been possible with an analogue computer...

)

Regards,
Simon

basil · Unread post by **basil** » 08 Jul 2006, 11:49

Thanks for the reply,I have just looked at the bottle and it is LHM+ so I shall use it 8)
I seem to have started an interesting discussion

________
NEW MEXICO MEDICAL MARIJUANA DISPENSARIES

Unread post by **alan s** » 08 Jul 2006, 12:45

Go for it; you'll be safe.
Doesn't take much to get the boys excited. $\:D/$ $\:D/$ $\:D/$

Alan S