In Reply to: But after a full-rebuild on a clutch system..., patquin [Profile/Gallery] , Tue, 25 Apr 2006 05:41:51

What people say is good about DOT 5 is that, unlike DOT 3 and 4, it's non-hygroscopic -- it doesn't absorb water.

But 3/4's hygroscopic properties are actually DESIRABLE and have been engineered into it. They absorb the water that's bound to get into any hydraulic system via the atmosphere, keeping it in suspension so that it's safely removed when you change the fluid.

DOT 5 doesn't absorb water, so what happens to the water that does get into your hydraulics? Since it's repelled by the DOT 5, it eventually comes together in little pockets that sit and sit and sit. There are two things bad about this: (1) when water gets hot, it turns to steam, which is highly compressible and thus a really lousy hydraulic medium; (2) the pockets of concentrated water are much more likely to cause spot rust-outs in your hydraulic plumbing.

These problems are addressed in systems designed specifically for DOT 5, but just pouring it into a system designed for 3/4 seems like a bad idea. Besides, it's gonna be a pain having to use two different kinds of hydraulic fluid for the brake and clutch systems -- sooner or later somebody's gonna mix them up, and then you'll have a huge mess!

Just my two cents, but for conventional hydraulics, DOT 5 seems like the answer to a question that doesn't need to be asked...

posted by 204.76.11...

• Alright, the old DOT 3,4, and 5 question..., Chaz, Mon, 24 Apr 2006 18:00:17
  • Re: Alright, the old DOT 3,4, and 5 question..., Ernesto , Tue, 25 Apr 2006 18:07:45
    • Thanks all.I stayed away from dot 5.n/m, Chaz, Wed, 26 Apr 2006 07:10:26
  • Re: Alright, the old DOT 3,4, and 5 question..., Ray Kopczynski, Mon, 24 Apr 2006 18:12:56
    • What about water absorption problems? nm, Chaz, Mon, 24 Apr 2006 18:35:00
      • Type 5 doesn't absorb water, but it still happens >>>, BobD, Mon, 24 Apr 2006 19:05:03
        • Re: DOT 3,4, and 5 question, Jim H, Tue, 25 Apr 2006 08:03:35
          • Re: DOT 3,4, and 5 question, kansas, Tue, 25 Apr 2006 08:52:59
        • Thanks Ray and Bob for the quick and great replies. n/m, Chaz, Mon, 24 Apr 2006 19:06:45
          • But after a full-rebuild on a clutch system..., patquin , Tue, 25 Apr 2006 05:41:51
            • ...I'd still stay with DOT 4, spiv, Tue, 25 Apr 2006 10:54:40 <-- Viewing This Message

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