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Older Diesels

Discussion in 'A6/S6/Allroad forum (C5 Chassis)' started by rhys084, Feb 24, 2014.

  1. rhys084
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    rhys084 Member

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    [Feb 24, 2014]
    Hi, me again with my questions.

    What makes the older diesels less refined and noisier?

    Take the 2.5TDI Tiptronic, at pulling away speeds it sounds quite loud. I've read things like 200ml of 2 stroke cures this as new diesel doesn't have the same lubrication as older diesel due to regulations, etc.

    But what part of the engine is actually making the noise and are there any other things that can be done to make it sound smoother?
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  3. desertstorm
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    desertstorm Well-Known Member

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    [Feb 24, 2014]
    The main difference in engine technology that has resulted in reduced noise is the multiple injections that occur this is a result of very fast acting Piezo injectors and high fuel pressures upto 2000 bar ( 30,000 PSI) also typically compression ratios have been lowered.
    On a 1.9 PD they ised to be 18.5-19 to 1 these days they are more like 16-17 to 1.

    Bosch Diesel Injection - Diesel Power Magazine

    It's very difficult to tell that my 3.0 V6 is a diesel. Even when cold it's not noisy and in the car you never hear any diesel rattling.

    Karl.
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  4. B5 BIKER
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    B5 BIKER Member

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    [Feb 24, 2014]
    So does the fact of adding 2 stroke make any difference?
    Any side affects or harm to it in the long run?
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  5. myth
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    myth Member

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    [Feb 24, 2014]
    Comparing a 2.5TDI with a 3.0 CR TDI could take hours and just breaking the top of the isberg.

    The 2.5TDI has an injection pump that sends diesel at the precise moment when the engine needs it, give or take a few degrees, due to timing piston correcting the timing. The process itself is noisy after current standards.
    Having a retarded timing means the injection pump sends diesel into the combustion chamber, it ignites, but the piston still has to move upwards. It's like wanting to make the piston move down, but it hasn't reached top dead centre yet.
    Having an advanced timing means the diesel gets into combustion chamber after the piston has reached top dead centre and already started moving down. The process it's relative silent, but the power delivered is lower.

    The classic injection pump is having a hard time adjusting the retarded and advanced timing. "Hard time" compared to newer injection systems :)


    The common rail on the other hand, is an injection pump that feeds the rail that connects the injectors with an equal pressure to all injectors. The timing is controlled directly by the computer. Theoretical, +- infinite. That's why a CR engine can start during winter with all glow plugs burnt out! The computer controls the timing as it wants, thus lowering the engine noise.


    Adding 2 stroke oil into diesel does not harm the engine whatsoever nor does not cure any problems you may have. The purpose of the oil is to lubricate the injection system because the newer diesel found in gas station doesn't have sulphur anymore, which was used to lubricate the injectors and injection pump. But the new diesel now has additives that replace sulphur and lubricates the system.
    Last edited: Feb 24, 2014
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  6. adamss24
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    adamss24 Well-Known Member

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    [Feb 24, 2014]
    The noise it's mostly increased CR and worn nozzles. I have a later BDG cam roller engine on my a6 project and it's very quiet, i reckon the heads have a lot to do with it ! Also larger nozzles without wear does make big difference as they can inject same amount of fuel in a shorter window of time so you get less clatter...
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