smart51
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| posted on 14/2/16 at 10:28 PM |
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clutch and power steering fluids
I've been looking at the service schedule for the MR2. It says to replace the brake fluid every 2 years but only to inspect the clutch and
power steering fluid. Is it not the same stuff? Is clutch and power steering fluid not hygrosopic? How do I inspect clutch and power steering
fluids?
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LBMEFM
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| posted on 15/2/16 at 06:19 AM |
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I would imagine that your MR2 uses Dot 5 which is Glycol based and therefore hygroscopic, i.e. it absorbs moisture. When the fluid gets hot the
moisture boils into vapour resulting in poor brake performance. The clutch fluid does not have to operate at high temps and therefore moisture
content is not so important. I think that steering pump oil is petroleum based. More modern types of brake fluid are silicon based and are not
hygroscopic. That's my understanding for what it's worth.
[Edited on 15/2/16 by LBMEFM]
[Edited on 15/2/16 by LBMEFM]
[Edited on 15/2/16 by LBMEFM]
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britishtrident
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| posted on 15/2/16 at 07:21 AM |
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Normal modern brake fluids are based on synthetic esters the brake fluid will be either DOT 4 or DOT 5.1. The clutch will use DOT 4.
Note DOT 5.1 not DOT 5 which is the only silicone based fluid and should not be used in systems filled with DOT 5.1 or DOT 4.
However DOT 4 and DOT 5.1 will mix with each other without causing problems.
These DOT 4 and DOT 5.1 fluids absorb water but the only the brake system will be subject to high temperatures.
The power steering will use an automatic transmission fluid (probablly to a GM Dexron specification) which are really hydraulic oils with some extreme
pressure and other additives.
Dexron power steering fluids come in synthetic or mineral oil based types using synthetic for a complete refill on a older power steering system
designed for mineral oil can cause leakage but the MR2 should be OK on either.
[Edited on 15/2/16 by britishtrident]
[I] “ What use our work, Bennet, if we cannot care for those we love? .”
― From BBC TV/Amazon's Ripper Street.
[/I]
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britishtrident
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| posted on 15/2/16 at 07:25 AM |
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quote:
Originally posted by LBMEFM
I would imagine that your MR2 uses Dot 5 which is Glycol based and therefore hygroscopic, i.e. it absorbs moisture. When the fluid gets hot the
moisture boils into vapour resulting in poor brake performance. The clutch fluid does not have to operate at high temps and therefore moisture
content is not so important. I think that steering pump oil is petroleum based. More modern types of brake fluid are silicon based and are not
hygroscopic. That's my understanding for what it's worth.
[Edited on 15/2/16 by LBMEFM]
[Edited on 15/2/16 by LBMEFM]
[Edited on 15/2/16 by LBMEFM]
I think you mean DOT5.1 not DOT5.
[I] “ What use our work, Bennet, if we cannot care for those we love? .”
― From BBC TV/Amazon's Ripper Street.
[/I]
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nick205
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| posted on 15/2/16 at 09:36 AM |
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IIRC my VAG cars have also been recommended to renew brake fluid every two years, but not the clutch or power steering fluid. As above, I suspect
it's the heat generated by the braking system that drives this and the comparative coolness of clutch and power steering systems that causes the
fluid to be left where it is. Not sure, but I believe there are testers for he water content of fluids - may be costly though if you're not a
garage using them all the time.
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britishtrident
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| posted on 15/2/16 at 09:48 PM |
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The reason for changing brake fluid is both DOT 4 and DOT 5.1 are hydroscopic. water is absorbed through the resevoir, seals and hoses.
Water absorbed in the fluid has a major impact on fluid boiling point.
DOT 5.1 starts out with a higher boiling point than DOT4 but it absorbs water more rapidly.
[I] “ What use our work, Bennet, if we cannot care for those we love? .”
― From BBC TV/Amazon's Ripper Street.
[/I]
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MikeRJ
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| posted on 16/2/16 at 08:33 AM |
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quote:
Originally posted by britishtrident
DOT 5.1 starts out with a higher boiling point than DOT4 but it absorbs water more rapidly.
Not always, you can buy "super" DOT4 fluids with a higher boiling point than DOT5.1. The higher the dry boiling point, the larger the
drop when the fluid gets contaminated.
The primary difference between DOT4 and DOT5.1 is viscosity; 5.1 has a lower viscosity and was developed for ABS systems where rapid fluid movement is
required.
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