C1256/1391--anyone ever try using DOT4 brake fluid?

Discussion in 'Gen 2 Prius Technical Discussion' started by TMR-JWAP, Feb 8, 2021.

  1. TMR-JWAP

    TMR-JWAP Senior Member

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    Someday, I'll remember to proofread the thread title before posting....

    Debating whether to try another experiment and curious if anyone has tried it yet.

    Over the last several months, our black 2005 has had the brake accumulator cycling on 9 second intervals. 3 seconds running then 6 seconds off, trying to maintain pressure. It finally coded on Friday 2/5 and we just parked it at the house. The weekend of 1/30, I had installed new axles and front hubs on this car. The brake accumulator assembly was in the planning stage, so it didn't come as a surprise. I finally got a chance to start looking at it yesterday, screen captured all the TechStream info and cleared the codes. The car is still doing the 9 second cycle time, and the accumulator pressure sensor is staying in the same voltage range as previously. Used it as my errand car all day yesterday with no problems.

    One thing in my plan was to perform a full brake fluid flush prior to digging into the accumulator replacement procedure to see if it changes the cycle time. After reading up on the accumulator job (probably way too much) and getting side tracked about brake fluids, I'm debating whether to do a DOT3 flush (OEM recommended fluid), check the results, and then flush again using DOT4. DOT3 viscosity is supposed to be <1500 and DOT4 <1800. Although there's some over lap, it would be interesting if I could find a specific brand DOT3 that is near 1500 and a specific brand DOT4 that is around 1800. Try them both to see how it affects accumulator leakage. Some references say DOT3 is recommended for ABS systems due to it being a bit thinner, allowing the ABS pulses to function better. Makes sense, but I suspect DOT4 shouldn't create any problems for an experiment.

    Trying to find viscosities of specific brands has been a bit elusive for me. Anyone have any input or recommendations?
     
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  2. mr_guy_mann

    mr_guy_mann Active Member

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    By itself, I wouldn't expect a different DOT fluid to have any significant affect on your problem. A leak is still a leak and the assembly is on its way to complete failure.

    There is a tiny chance that IF a piece of debris is stuck in one if the valves, that a few hard ABS stops MIGHT dislodge it and then you could flush the system out. But I doubt that would work. I have seen only a few failures of ABS units over 30 years, and replacement has been the only cure.

    Posted via the PriusChat mobile app.
     
  3. sam spade 2

    sam spade 2 Senior Member

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    Thank you.
    It has been way too long since anyone has come up with a new thing to trigger an OCD episode. :eek:
    :ROFLMAO::ROFLMAO:

    Look for some that is labeled DOT 3/4 and then you won't have to worry about it !!! :whistle:
     
  4. TMR-JWAP

    TMR-JWAP Senior Member

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    Sam....not all brake fluids use the same exact components. Two different manufacturers can very easily have different compositions, which can have different viscosities. The spec for DOT4 is <1800. I want one closer to 1800, not 1000. There is even DOT4 available that is 700ish.
     
  5. sam spade 2

    sam spade 2 Senior Member

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    "I want......"
    Like I said, OCD.
    The difference isn't important in any imaginable real world circumstances.
    Really it is NOT.
     
  6. TMR-JWAP

    TMR-JWAP Senior Member

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    Reading comprehension....check it out.

    From post number 1:
    Debating whether to try another experiment and curious if anyone has tried it yet.... and....
    Although there's some over lap, it would be interesting if I could find a specific brand DOT3 that is near 1500 and a specific brand DOT4 that is around 1800. Try them both to see how it affects accumulator leakage.

    It's not that difficult to understand that all I'm looking for is some input if anyone knows of any charts/data/research that shows different brands of brake fluid and their actual viscosities. A bit similar to the information that is out there for various engine oils and transmission fluids.

    Although not interesting to you, you still feel the need to throw in your opinion, and that's fine. It's interesting to me, and that's all that matters. I know for fact the ABS pump cycles every 9 seconds in this car. What I don't know, is what the current viscosity of the brake fluid is, or if finding a DOT4 @1800ish will make it cycle every 10 seconds or 15 seconds or 20 seconds. Could flushing the system with a brake fluid that is twice the current viscosity change the leakage rate and improve that cycle time? The only way to find out for sure is to try it. I have the time, the knowledge and the equipment. All I need is viscosity information, which may not be available. If not, I'll find something else to do. I have a project list a mile long. You enjoy spending time yanking people's chains on forums. Maybe I enjoy doing things like this. To each, their own. We all have hobbies. This doesn't have to be complicated.
     
    #6 TMR-JWAP, Feb 8, 2021
    Last edited: Feb 8, 2021
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  7. sam spade 2

    sam spade 2 Senior Member

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    You seem to have a problem similar to "reading comprehension".
    I feel a need to point out when people say things that are simply WRONG or appear to be wasting their time on something that really is inconsequential.........because they often don't KNOW that it is a waste of time.

    In this case, it might be or might not be.

    This is not "yanking anybody's chain".
    No offense is intended. If you choose to TAKE offense, that is your problem.
     
  8. ChapmanF

    ChapmanF Senior Member

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    If your intention really is to save people from making mistakes or going down rabbit holes, it would be much more in line with your intention to make sure that your posts include citations to reliable sources that support your opinion. The simple reason is that, if you don't, say member A doesn't KNOW that idea B is a waste of time, and you jump in and post your personal opinion that it is, and afterward member A still doesn't know that. Even using capital letters in your opinion does not help as much as citing a reliable source.

    It's worth remembering that this is true even if your opinion is correct. The operative question is, have you supplied other members, who do not know you from Adam, with adequate reason to believe your opinion is correct?

    People might put more stock in a bare statement of your opinion on an EE technology question, just because a number of your posts mention being an EET for 50+ years, so people with nothing else to go on may rely on the credential as a sign of your background in that area. Even there, giving good supporting citations only helps, for a few different reasons:

    • This is the internet, so no one really knows whether your name is Sam, you are an EET, or anything else about you;
    • Some may believe that different people can hold the same credential without being equally good at what they do;
    • People may assume that you are extra familiar with the literature of your own field and could very easily supply on-point citations supporting your opinions, and therefore wonder what it means if you haven't.

    Bu of course in areas other than EE technology, you don't have the credential to fall back on; at least I don't remember you posting about your professional experience in ABS brake system engineering or materials science in hydraulic fluids.

    That doesn't in any way mean that you can't be knowledgeable in some area outside your main field. It just means that showing your sources and your work is the only way available to you of establishing that.
     
    #8 ChapmanF, Feb 9, 2021
    Last edited: Feb 9, 2021
  9. sam spade 2

    sam spade 2 Senior Member

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    Everything posted here is an OPINION.
    I have much better things to do with my time than to look up references for things I have learned the hard way over my 74 years.
    Anyone who REALLY cares can do their own research.
    Meaning real research, not searching Internet forums.
     
  10. ChapmanF

    ChapmanF Senior Member

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    There are people coming to PriusChat every day who really care, and a lot of them do end up getting good information, even though it is an internet forum.

    Part of how they do that is by looking over the various opinions and making judgments as to which ones are worth their attention. Bringing the goods with your opinion does take some time that you might rather use some other way. But then, so does posting opinions that are likely to be dismissed because you didn't.
     
  11. Elektroingenieur

    Elektroingenieur Senior Member

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    Here are two sources in which suppliers state the kinematic viscosities of their DOT 3 and DOT 4 brake fluids, rather than just referring to the limits in FMVSS 116 or other standards:
    Of the two, only MAG 1 discloses the viscosity at 100 °C, which is the same for both of their formulations.
     
  12. ChapmanF

    ChapmanF Senior Member

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    I can imagine fluid reaching or exceeding 100 ℃ at a wheel cylinder; I wonder what the comparative viscosities would be at the more everyday temperatures seen around the valves of the actuator. Somewhere between −40 ℃ and 100 ℃ would be nice.

    I guess maybe the takeaway is that if they are not any more different than that at −40 ℃, maybe the difference isn't going to be all that noteworthy anywhere.
     
  13. TMR-JWAP

    TMR-JWAP Senior Member

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    Thanks Elek! Looks like one data point on the DOT4 ESP is probably a misprint, but in the big scheme, taking normal driving weather conditions and temperatures into account, all the blend viscosities are likely to be similar or at least similar enough and low enough that my 'clock' wouldn't detect the difference on cycle time. Some you win some you don't. Guess I'll have to try some Mobil 1 20W-50, see what that does..............










    wonder how many people are getting ready to furiously type on the keyboard right now
     
  14. Paul Schenck

    Paul Schenck Active Member

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    All I know is dot5
    Can cause failure because it’s not glycol based.


    iPhone ?
     
  15. mr_guy_mann

    mr_guy_mann Active Member

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    The technician training classes I took years ago stated that DOT 5 wasn't recommended for any ABS equipped cars because that fluid "foams" (produces bubbles) when subject to rapid movement and pressure changes (what happens in the hydraulic unit).

    Posted via the PriusChat mobile app.
     
  16. sam spade 2

    sam spade 2 Senior Member

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    And why exactly did you think saying that would be at all helpful to anybody ?
    If Dot 5 is introduced into a system that did not originally have it, it will form something like axle grease when it meets the Dot 3/4 residue.
    Not that it "can" fail, but it WILL.
     
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  17. Paul Schenck

    Paul Schenck Active Member

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    Hey Sam, I only have 63 years of experience so I certainly don’t match your 74. I didn’t see anywhere in the tread the hazard of Dot 5 and wanted readers to know switching from one break fluid to another should not be done without understanding that although 3 to 4 may be done. Switching to Dot 5 will cause failure.


    iPhone ?
     
  18. JimboPalmer

    JimboPalmer Tsar of all the Rushers

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    I am impressed by the people in this thread who don't use the regenerative braking available in their Prius, which is not based on brake fluid.

    I had a pedestrian today leap back into traffic to pick up a ballpoint pen he had dropped, so I did use my brake fluid today. Proper planning (by all involved) means you never use your friction brakes above 10 MPH.
     
  19. sam spade 2

    sam spade 2 Senior Member

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    I'm sorry that I mis-understood your intent.
    I think it was because of the way that your comment was formatted.
     
  20. TMR-JWAP

    TMR-JWAP Senior Member

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    A bit of an update. Maybe this can help someone avoid a major repair. I decided I was going to try a few things before getting into a full actuator swap. Took the accumulator off a salvage yard actuator (I have a few) and installed it into the car.

    This can be done in less than an hour, without disconnecting any brake lines. Just remove the cowl and windshield wiper assembly. Used techstream to bleed all pressure from the system and then pulled the ABS relays so the pump couldn't start. Then swapped the accumulator tank.

    Removed the vast majority of the brake fluid from the reservoir using one of these:

    Progressive™ Flavor Injector | Bed Bath & Beyond (bedbathandbeyond.com)

    and then filled reservoir with fresh DOT3. Did not perform any additional brake bleeding.

    Cycle time on the actuator went from 9 seconds ( 3 seconds run, 6 seconds off) to averaging 43 seconds. I used the stopwatch/lap function on my phone to measure countless cycles over 2 days while watching pressure sensor reading on techstream. Reset the timer every time the pump started. Sometimes the actuator wouldn't bleed off at all until I cycled the brake pedal, so those cycles weren't counted. Took the car for several drives and each time returned to the house and did more timing checks, using the lap function each time the pump started. Very consistent results.

    Being curious, I re-installed the original pressure tank over the weekend. Same result. 43 second average over 30 cycles. Maybe next weekend I'll swap the brake fluid in the reservoir again and do a full bleed/flush to see what happens. Or just leave it the heck alone and call it a success. Somewhere around August will be the three year point of having purchased this car. I have no accurate idea of the age of the fluid that was in the car, but potentially, the difference between old fluid and new fluid can be enough to make a difference. If that can make a difference, then it seems likely anything with a different viscosity can make a difference. Isn't that why, for a long time, DOT3 was recommended over DOT4 for early ABS systems? The DOT4, being thicker, didn't bleed off fast enough for proper brake pulsing?

    So perhaps the questions that were mentioned in post 6 have some legs to stand on. As Chef Gordon Ramsay frequently says, perhaps someone else in this thread can piss off.

    As for this (from the beginning of the post):
    Maybe this can help someone avoid a major repair.

    Keep up with your brake fluid replacement schedule. It may (or may not) make the difference between needing an actuator replacement (or not)..one example does not make a surefire solution, but it does provide possible temporary relief ..
     
    #20 TMR-JWAP, Apr 13, 2021
    Last edited: Apr 13, 2021
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