For LHS Cars
Alternate Fluids For LHS Cars
Specifications For Fluids Used In LHS Cars
Original Fluids For LHM Cars
Alternate Fluids For LHM Cars
Specifications For Fluids Used In LHM Cars
Fluid Changes and Flushing
Tony Jackson began supplying the Citroën virtual community with this summary many years ago. Since then is has seen numerous edits and modifications. Keeping old cars in running condition is difficult enough, but these Citroens offer the extra challenge of hydropneumatic systems involving braking, steering, suspension and transmission control.
Given the increasing difficulty in finding original specification hydraulic fluids, owners have often relied on ingenuity to devise alternatives. LHS is now made periodically by only one company, Pentosin. The supply is sporatic and prices can vary widely as inventories dwindle. LHM is not available everywhere, though prices seem stable right now. The Fluid Summary is an attempt to provide an updatable source of information on older as well as ongoing trials.
It must be stressed that the authors do not in any way wish to take responsibility for consequences arising from the use of any of this information. Readers are hereby informed that all of this work is fully experimental in nature and any actions taken by readers will be considered as on their own volition. In other words USE THIS INFORMATION AT YOUR OWN RISK.
While original fluids are not always readily at hand, in most cases
it is best for your car to use them. One exception might be a car that
is undergoing restoration and is prone to leaks.
We invite the Citroën community to offer us
information on your efforts. This document is by no means complete or
final. As you can see by the following chapters, charts and articles,
there are many
gaps in our knowledge. Please send your contributions to the authors.
It is going through constant changes, so please check back regularly.
Fluids for LHS CarsOriginal Fluids For LHS Cars Top
In late 1964, synthetic based LHS (Liquide Hydraulique Synthetique) supplanted the old formula. LHS was apparently manufactured only by Eugene Kuhlmann in France and Deutsche Pentosin Werke in Germany. All other suppliers bought from one of them and packaged under their own labels. Some problems subsided, but hygroscopy was still an issue. A list of approved fluids was issued by Citroen in Technical Note No. 29-D, dated September, 1964. The note also specified four seals that had to be changed to make the cars compatible with the new fluid. The old ones were of natural rubber and the replacements were of EPDM, a newly developed synthetic. Here is a copy of the technical note. Included are the old and new part numbers for the four seals.Old and new seal numbers (from Tech Note 29-D, September, 1964) and their use
||Security Valve (ID)
7 Cylinder Pump (DS)
||7 Cylinder Pump (DS)
||Rear Wheel Cylinder, Saloon
||Rear Wheel Cylinder, Break
Cars sold in the United States and Canada faced more difficulites.
of these fluids were available. Instead, Citroen specified standard
brake fluids. Lockheed 70R1 grade fluid was initially listed in the
owners' manuals to
comply with standardizing Federal regulations. By 1966 the factory
approved any fluid complying with specification SAE 70R3, including
Mobil Super HD, Delco Super 11, Lockheed Wagner 21B,
Mopar Hi Temp. SAE 70R3 was later replaced with DOT 3. Each new fluid
provided improvements, especially higher boiling points, but even when
DOT 3 came along, it still lacked sufficient viscosity and lubricity
for best ride performance, transmission shifting and control of wear.
Everywhere except in the US production changed in 1966 to use a green-dyed mineral fluid, LHM, which did not take up water, and which has proven highly successful ever since. LHM was not compatible with the seals used in cars built previously, so the hydraulic component color was changed to green as a warning. Cars sold in the US changed to LHM in the middle of the 1969 model year due to delays in governmental certification, so consequently, early 1969 model cars in the U.S. still used LHS. Again, the color of the hydraulic components is the tell tale; black is for LHS and green signified that the car used LHM.
|LHM was introduced at the following serial numbers for all except U.S. export models||LHM for US export models was introduced at the following serial numbers|
|DS19A-H||4 316 000||DS19A-H||4 330 000|
|DS19A-M||4 442 000||DS20-H||4 332 001|
|DS21-H||4 376 200||DS20-M||4 451 001|
|DS21-M||4 473 100||DS21-H (including cabriolet)||4 621 000|
|Cabriolet DS21-H||4 376 050||DS21-M (including. cabriolet)||4 490 001|
|Cabriolet DS21-M||4 473 020||ID19B||3 794 600|
|Cabriolet Chapron DS21-H||4 376 000||ID20||3 820 001|
|Cabriolet Chapron DS21-M||4 473 000||Break ID19FA-M||3 546 800|
|ID19B||3 710 001||Break ID19FHA||3 980 380|
|Familiale ID19FA||3 535 000||Break ID20F||3 980 501|
|Break, Ambulance, etc. ID19FA||3 536 000||Break ID20FH||3 985 001|
|Familiale ID21F||3 554 000||Break ID21F||3 561 600|
|Break, Ambulance, etc. 21F||3 554 500||Break ID21FH||3 575 350|
Factory Seal part number interchange chart for LHS and LHM vehicles, dated June 1969Alternate Fluids For LHS Cars Top
Even so, several owners have run cars
satisfactorily on silicone DOT 5.
Some add an additional filter between the pump and reservoir to collect
material. Some report problems caused by its
very high electrical insulating tendencies. Weeping around the brake
cause trouble with the brake switch. Steps must be taken to isolate
part. One owner installed a pressure activated switch on one of the
front calipers. Trouble with contamination of ignition points has also
Many owners convert their systems to electronic, thereby eliminating
This mixture has been used for some time without problems, except in cold climates. If the car is to be used while ambient temperatures are below the freezing point, the castor oil fluid should be drained and replaced with DOT 3 brake fluid and the brakes bled. This is to prevent any castor oil separating out and freezing in lines or components. When warm weather resumes, just add 4 oz. of castor oil. Castrol R racing oil (used by some racing motorcycles) is one source. Model engine or aircraft suppliers are another. Unfortunately, the advent of synthetic oils has made it harder to source. Castor oil is also available in health stores with unpredictable prices.
DOT 4 brake fluid can be used, but has a tendency to absorb water more quickly, so it's boiling point decreases faster than DOT 3. Because it is open to the atmosphere, this is an important consideration in our systems.Converting to LHM
Biostar 32 was nearest to the Citroën specs. However, its rather high pour point and low viscosity index still gave problems when used it in very cold conditions. Biostar is now unavailable, but other companies offer similar products, such as Hydrosafe. The comparison chart, below, now lists the Hydrosafe product rather than Biostar. Note also, there is no specification for boiling point.
Now that rapeseed has been in experimental use for some time, several problems have cropped up. It is proven to be fatal to cars made before 1963 unless every seal has been replaced. This is because those older cars had seals made of natural rubber, which is not compatible. These cars also suffered from decompostion of rubber parts adjacent to hydraulics, such as suspension bump pads. We have now found that some cars that used rapeseed oils have not fared as well due to accelerated wear in moving parts. Even though some owners contunue to use it, for these reasons we can no longer recommend the use of canola base fluids.PAG and Brake Fluid
Still, lubricity is vastly superior to pure brake fluid. It should be noted that PAG is actually used in many brake fluid formulations, particularly DOT 5.1. We do recommend that you test several brands of DOT 3 brake fluid before using to determine solubility.With the availability of genuine LHS becoming spotty, we must continue our work on viable sustitutes. While each have merit, they also have drawbacks. Pentosin refuses to disclose the formula for LHS, so anything we use must be used with caution. The only thing they have told us is that one of the components is hard to source. That is why we can not recommend the use of any of the substitutes. Unless you are willing to assume the risks of damage to your car or possibly of failures of vital systems, especially the brakes, you should use the factory recommended fluids.
|These specifications are harvested from other sites. They are not intended for use as MSDS or true data sheets, as many of these fluids vary greatly by manufacturer!|
For Comparison Only. Do Not Use!
|LHS 2||DOT 3
||DOT 5.1||DOT 5 Silicone based brake fluid||Hydro-Safe ISO-VG-Premium 32 (rapeseed
9.25% Castor Oil/DOT 3
|DOT 3/ PAG 150
||Amber||Blue/Purple||Clear, light amber
|Density at 15C||g/cm3||0.830||1.007||?||1.05||?||.88||~1||No tests,
|Viscosity at -40C||cSt||<1200||?||1065||900
|Viscosity at 20C||cSt||?||32.4||?||?||?||?||34.7||be about half
|Viscosity at 40C||cSt||18||14.5-16.5||7.1||?||?||30.7||?||way between
|Viscosity at 100C||cSt||6.3||4.5-5||2.0||1.5
|Pour point||Deg C||-62||?||?||?||?||-40||?||LHS
Wet is 3.7% water
|Deg C||255||?||205 dry
|?||?||Unknown, but should be near DOT 3|
|Flash point||Deg C||135||99||149||?||204||236||?|
Fluid for LHM CarsOriginal Fluids For LHM Cars Top
Properties of LHM+ (the latest version, fully compatible with original LHM). Recommended by Citroën.
The actual specifications for LHM differed from the earlier version of "red oil" in one important aspect, VI (viscosity index). The VI represents how much a fluid's viscosity changes with temperature. The higher the number, the more constant the viscosity will remain across a given temperature range. As of 2/97, MilSpec 5606(F) was supplanted by 5606(G). The major improvement was in the area of low temperature viscosity. Since then, the specification has again changed and is now (H). The VI for LHM is over 350, while the older 5606(F) red oil was around 300. The VI of the new MIL-H-5606(H) is now above 370, surpassing LHM. For comparison, the VI for Dexron (regardless of type) is only about 200. However, the viscosity of red oil is lower than LHM at all temperatures.A comparison of MilSpec 5606(H) and LHM+:
Generally speaking, the vast majority of mineral oil based hydraulic fluids are fully compatible with the seals in LHM cars. I have added Shell Tellus to the list below for comparison purposes. However, most of them do not have viscosity characteristics the hydraulic systems were designed for. They can adversely effect shift characteristics in (BVH) equipped cars and if extreme, will even cause suspension behavior and steering problems. Fluids with low VI will cause problems with temperature fluctuations. A good minimum would be 280. LHS2 has a VI index of 280 and a cST rating of 14 at 40c. LHM+ has VI index of 350 and a cST value of 18 at 40C. When the factory went from LHS2 to LHM the only thing that was changed was the rubber seal composition. The actual design of the various hydraulic components remained unchanged. There is sufficient allowance in the system design that a change in fluid cST at 40C from 12 to 20 will have little to no effect on basic performance or system feel.
|These specifications are harvested from other sites. They are not intended for use as MSDS or true data sheets!|
|ARAL Vitamol ZH-M||Shell Tellus 22||Exxon Univis 13||Kendall Hyken Glacial Blue||Lubriplate 70
|Density at 15C||Kg/L||0.830||0.857||0.825||0.825||0.86||.861||.866||.855||.87
|Viscosity at -40C||cSt||<1200||1050||<1100||1500||600||6000 (?)||371||2840
|Viscosity at -20C||cSt||230||240
|Viscosity at 0C||cSt||75||180||338|
|Viscosity at 20C||cSt||32||~32|
|Viscosity at 40C||cSt||18||18||18.6||36.8||13.2||16||22||13.5||14.9||16
|Viscosity at 50C||cSt||14.3|
|Viscosity at 100C||cSt||6.3||6.0||>6||7.65||5.0||~4.2||4.3||5.3||4.4||6
|Pour point||Deg C||-62||-62||<-62||-45||-60||-40||-30||-60||-60||-56.7
|Boiling point||Deg C||255||288
|Flash point||Deg C||135||82||140||204||100||170||93.3
For glycol based fluids the material of choice is ethylene propylene (epm, pdm, epdm). Introduced in 1964, it still has the best resistance to brake fluid. A new compound that has been recently introduced and shows promise as being suitable for both glycol and petroleum based fluid is Aflas (TFE Propylene/trademarked 3M).
For Petroleum based fluids (LHM, Dexron, 5606 Spec, etc.) the following materials are the most widely used: Fluorocarbon based, (Vinylidene fluoride-hexafluoropropylene) also know under the trade name Viton (and others) and Nitrile (NBR or Buna N, Acrylonitrile-Butadiene Copolymers). Of the two Viton has the best mechanical strength/temperature resistance and is much more expensive compared to Buna N. While there are others, the above two are the most common.
The seals in our cars are of two types-static and dynamic. Static seals are those where the sealing faces do not move. Dynamic seals are those where one or more of the sealing faces moves relative to the other. To list a few, the power steering rack, suspension cylinders, brake pistons, clutch engagement control/steering speed control (in SM's), height control valves, rear brake articulating joints on ID/DS series are all examples of dynamic sealing points. The high pressure pump has one dynamic seal, though it is a metal to metal seal at its driveshaft. The suspension sphere diaphragm is a special kind of seal and presents real problems from a design standpoint. Not only must it be resistant to the fluid in use, it also has to have extremely low gas permeability, excellent flexibility and tear resistance over a wide range of temperatures and pressures.
When Citroën introduced LHM in 1966, they encountered serious high temperature problems with the diaphragm material during the first couple of years, primarily with gas permeation. This problem has been almost completely eliminated in the latest cars, such as the C5. The diaphragms are now 2 ply.
These are the three commonly found compounds in our systems built since the introduction of LHS and their usage (earlier cars used natural rubber)
LHM systems use a flushing agent called "Hydraurincage" ("hydro-rinse-ahj"). It can be used full strength for full effect, or it can be mixed. Hydraurincage can be left in the system for as long as 3,000 miles/5,000km. before it needs to be removed and fresh fluid installed. It can be hard to find in the US in particular, but Citroen part suppliers stock it. It does not need to be used frequently. It is most effective on cars that have been taken out of long storage or that have had a history of neglect. When in the system, frequent filter cleanings will be needed. Gasoline can be used to clean components (use great care) or mineral spirits.
Never use Hydraurincage in cars using LHS fluid.
Those with D's with glycol-based fluids (LHS) need to be more diligent regarding changes. When the car rises, fluid moves out of the reservoir drawing air in. Moisture in the air is absorbed by the fluid. This problem is aggravated in moist climates and lessened in dry greatly increases the potential for corrosion in the system-especially on parts and areas where there is little movement of the fluid, such as wheel cylinders. High moisture content drastically lowers boiling point of your fluid which can braking dangerous as it actually can turn into compressible vapor. Several owners have tried alternative fluids to counteract these problems. Like LHM, viscosity modifiers, lubrication additives and corrosion inhibitors all degrade over time. All these things happen faster in our cars than in typical closed systems. Because of higher working pressures, constant circulation and influx of moisture laden air, the factory recommended change interval was 18,000 miles/30,000 km. We recommend every two years in dry climates and light use and every year in humid conditions or heavy use regardless of mileage. In cars that are not used frequently, those intervals might be extended.
The flushing agent specified by Citroen for LHS cars is hexylene glycol. It should only be left in for 20 miles/30km if used full strength. Mark Bardenwerper used it in a U.S. specification ID 19 with excellent results. As it was rather expensive, he drained and added only about a quart instead of a complete change and left it in for double the time. He did have to clean his filter a few extra times. His steering had better feel and power, for one thing.
Some owners used pure brake fluid and a little alcohol. I would not recommend using alcohol as it will not lubricate at all and could cause damage, though alcohol or soapy water can also be used to clean LHS components during repairs (parts must be thoroughly dried before reassembly).Credits Top