# Car question: What is the LHM fluid?

**URL:** <https://boards.straightdope.com/t/car-question-what-is-the-lhm-fluid/255735>\
**Category:** Factual Questions\
**Created:** [July 18, 2004, 11:50pm UTC](https://boards.straightdope.com/t/car-question-what-is-the-lhm-fluid/255735 "2004-07-18T23:50:45Z")\
**Posts on this page:** 3\
**Page:** 1

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**Author:** ![Dog80](https://avatars.discourse-cdn.com/v4/letter/d/6bbea6/32.png) [@Dog80](https://boards.straightdope.com/u/Dog80)\
**Post date:** [July 18, 2004, 11:50pm UTC](https://boards.straightdope.com/t/car-question-what-is-the-lhm-fluid/255735/1 "2004-07-18T23:50:45Z")

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I am talking about Citroen’s LHM fluid that is used in brakes and hydropneumatic suspensions. What goes into that fluid? Is it similar to a DOT 3 or DOT 4 brake fluid? Is there another oil I could use as a substitute in an emergency?

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**Author:** ![mike1dog](https://avatars.discourse-cdn.com/v4/letter/m/ba9def/32.png) [@mike1dog](https://boards.straightdope.com/u/mike1dog)\
**Post date:** [July 18, 2004, 11:55pm UTC](https://boards.straightdope.com/t/car-question-what-is-the-lhm-fluid/255735/2 "2004-07-18T23:55:24Z")

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I know very little about citroens since they’re not sold in the U.S., but I can tell you that there is a lot of difference between hydraulic fluids. We once had a customer who went through power steering pumps and gears like crazy, all because he used some sort of generic hydraulic fluid for tractors in his fleet of trucks. We finally convinced him to use what the manuals called for, and he never had another problem.

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**Author:** ![donkeyoatey](https://avatars.discourse-cdn.com/v4/letter/d/e47c2d/32.png) [@donkeyoatey](https://boards.straightdope.com/u/donkeyoatey)\
**Post date:** [July 19, 2004, 12:42am UTC](https://boards.straightdope.com/t/car-question-what-is-the-lhm-fluid/255735/3 "2004-07-19T00:42:25Z")

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Check [this page](http://www.mg-sportcars.co.uk/Brake_Fluidsl_FA_Questions.htm), **Dog80**. It looks like it isn’t compatible with any other brake fluid.

> [@](#):
>
> LHM is NOT compatible with conventional brake systems, nor are conventional Brake Fluids compatible with systems requiring mineral oil. Failure to use the correct fluid may result in total brake failure.