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  #1  
Old 09-25-2007, 09:56 PM
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Knocking at start

When I start her up, warm or cold, I hear a fairly loud knocking, the after about one or two seconds, oil pressure builds on the guage and the knocking goes away (or at least dissipates a whole lot). Is this normal? How long does it usually take for oil pressure to build at startup in a 617 turbo?
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Old 09-25-2007, 10:59 PM
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for me in my 1981 240d it takes about two seconds, and has a pretty persistant knock at startup.
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Old 08-25-2008, 02:27 AM
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sounds pretty normal to me. my 1980 240d makes a pretty distinct knock at startup and oil pressure builds within 2-3 seconds. it would be my guess that with a turbo your oil pressure may have a slightly longer lag, because of all the added oil lines to the turbo bearings. although we're probably talking miliseconds if anything.
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Old 08-25-2008, 02:38 AM
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Sir, That seems pretty much par for the course at 272K+miles. Tolerences in both the oil pump and the mains (which is where the noise eminates) have increased. Nothing to be alarmed about. Good quality oil and a full crankcase of it is your best bet. When oil levels are lower than full, especially with a pump having been quite well seasoned in, it surely could take a little longer to pump up. The sooner, the better
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Old 08-25-2008, 02:52 AM
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you may want to try a heavier oil or an additive like stp. I'm pushing 350K on my diesel and even after an oil change where the oil takes a few seconds to get back up to pressure, have no knock. Sounds like they said above you have a rod bearing that's got more clearance then it should. Where does your oil pressure run when the engine is hot? Does the knock come back every time you start the car or only cold. Can you hear the knock fade as oil pressure comes up, or does it just fade after the pressure reaches 3bar?
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