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Thread: Use silicone vacuum hoses???

  1. #1
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    Default Use silicone vacuum hoses???

    I have been having rough idle problems and have found a lot of useful threads about diagnosing the problem in my 1992 BMW 525i E34 M50. After reading them I went under the hood and ended up finding some loose, hardened and brittle vacuum hoses in the area of the intake.

    I am interested in replacing my vacuum hoses with those colored silicone hoses. I know a lot of Porsche guys do that. I looked for an archive on this and could not find any. Can anyone direct me to an archive on them? Specifically, do they commpare to OEM in terms of performance, and longevity? Does anyone know the size of the vacuum hose reuired for my engine? I heard that they are 3.5MM or 8 MM hoses.

  2. #2
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    Porsche/audi/vw guys replace vacuum hoses with silicone because those cars are turbo and therefore most of their "vacuum" hoses are "boost" hoses. They are prone to splitting and such - you can replace them if you want, but they are expensive typically $6 - 8 a foot.

  3. #3
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    Quote Originally Posted by Jon K
    Porsche/audi/vw guys replace vacuum hoses with silicone because those cars are turbo and therefore most of their "vacuum" hoses are "boost" hoses. They are prone to splitting and such - you can replace them if you want, but they are expensive typically $6 - 8 a foot.
    The only way I would switch to silicone hoses from OEM rubber hoses is with the expectation that they would last a lot longer. Once I remedy these vacuum leaks, I really do not want to deal them again. I want to drive my car not repair it. I have realistic expectations that my car that is nearly 15 years old and has over 200,000 miles on it will have a lot of repair issues. However, I want to be smart about it and reduce repeat maintenance as much as I can.

    I found 3 vacuum leaks on my 1992 BMW 525i E34 M50 and I have not even checked the hoses around the ICV under the intake manifold yet. The rubber hoses are stretching where they are pushed over the fittings so that the fit is no longer snug and air tight. I just pulled the hoses off and cut them back about 1/2 inch and put the hoses back on. Another rubber hose was hardened to the point that is was no longer snug around the fitting. I put a hose clamp on this one. These are just a temporary fixes until I figure out which way I want to go - OEM rubber or custom silicone.

    Do you know whether silicone will last substantially longer than rubber hoses and perform at as well or better? Also, do happen to know the inside diameter of the vacuum hoses on my engine?

  4. #4
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    for some of the small ones i like to use fuel hose. thats what we did on evap leaks when i was a chrysler tech. never before have i seen 3 year old cars with rubber hoses splitting. My 1990 325i never had a vaccum leak. But yea, fuel hose will be cheaper than silicone and will never break, its reinforced.

  5. #5
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    Quote Originally Posted by markus
    for some of the small ones i like to use fuel hose. thats what we did on evap leaks when i was a chrysler tech. never before have i seen 3 year old cars with rubber hoses splitting. My 1990 325i never had a vaccum leak. But yea, fuel hose will be cheaper than silicone and will never break, its reinforced.
    So the reinforced fuel lines are more durable then the rubber only vacuum lines. Are they also more durable than silicone vacumm lines? Will they maintain their snugness around the fitting over time? Don't the fuel lines get hard and brittle over time?

    Do you happen to know the inside diameter of the vacuum lines on my M50 engine?

  6. #6
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    I replced all my vacuum hoses with reinforced fuel hoses instead of using vacuum hoses or sillicone hoses. The smaller hoses are covered with braided cloth and the larger ones are reinforced inside the rubber wall. It also fixed a vacuum leak proble that was causing a hunting idle.

    Thanks for the responses!
    92 525i w/ Eibach lowering, Bilsteins, KMAC, Dinan chip, low temp coolant switch, K&N replacement air filter, UUC short shifter, RD strut brace, blacked out, 17" Borbets

  7. #7
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    I replced all my vacuum hoses with reinforced fuel hoses instead of using vacuum hoses or sillicone hoses. The smaller hoses are covered with braided cloth and the larger ones are reinforced inside the rubber wall. It also fixed a vacuum leak problem that was causing a hunting idle.

    Thanks for the responses!
    92 525i w/ Eibach lowering, Bilsteins, KMAC, Dinan chip, low temp coolant switch, K&N replacement air filter, UUC short shifter, RD strut brace, blacked out, 17" Borbets

  8. #8
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    Use black rubbers...Its vacuum lines..... psst(I get it for free)

  9. #9
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    Quote Originally Posted by aston_jag_tech
    Use black rubbers...Its vacuum lines..... psst(I get it for free)
    The fuel lines are black rubber, just reinforced to last longer atleast in theory! Plus they are very inexpensive. Sorry if there was a joke or hint there that I missed.
    92 525i w/ Eibach lowering, Bilsteins, KMAC, Dinan chip, low temp coolant switch, K&N replacement air filter, UUC short shifter, RD strut brace, blacked out, 17" Borbets

  10. #10
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    Quote Originally Posted by bissellh
    Sorry if there was a joke or hint there that I missed.
    You better be sorry!


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