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Old 02-03-2005, 12:19 PM
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oil in vacuum system on 300sd

I am looking at a 1980 300SD that's for sale locally. Everything seems to be okay on it except that it has oil in the vacuum lines. So my question is: What is the best route taken to rectify this problem? Should I rebuild the vacuum pump as a start? How can I get the oil out of the vacuum lines?

Peter Koskinen
Chapel Hill, NC
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Old 02-03-2005, 05:34 PM
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I would think if you repaired the vacuum pump diaphram, the repaired pump would suck most of the oil out of the system and back into the engine where it belongs. I'm not sure if there is any other way for oil to get in the vacuum system except through a failed vacuum pump diaphram?

Alternatively, you could disconnect each vacuum line that has oil at each end (rubber connectors) and suck some type of solvent through with a mighty vac. Once flushed out you would need to dry it out with compressed air.

Is the oil causing problems? Perhaps any problems you are seeing with vacuum is not due the oil, but due to an inoperable vacuum pump.

Good luck.
1998 C280
1982 240D Manual - Sold
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Old 02-03-2005, 06:05 PM
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Location: RI shore
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a good way to get oil out of the plastic vacuum lines is a pipe cleaner dragged through with a little string. The rubber lines are so cheap that..... But looking ata car to purchase, you must remember that one reason oil gets in the vacuum lines is when an engine has a lot of blowby and it forces that blowby into the vacuum pump and then down the vacuum lines. You probably don't want to buy a car with a lot of blowby, so check for that carefully.
'82 300SD - 361K mi - "Blue"

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listen, look, .........and duck.
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Old 02-03-2005, 08:04 PM
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Can't a failing vacuum shut-off diaphram on the injection pump cause oil to be sucked up into the system? Pull the lines at the shutoff valve on the ignition switch (if the owner will let you) and see if there is oil there being pulled from the diaphram and into the rest of the system.
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Old 02-03-2005, 08:10 PM
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jhal's probably onto it...

I had a 80 300D that had oil on top of the radio when I pulled the dash. it was the vacuum shutoff diaphragm leaking. If you've got a mity vac put it on the line and see if it leaks.
'99 S420 - Mommies
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'85 300SD Silver - Sold
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Old 02-03-2005, 08:57 PM
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Sometimes I don't think of the easiest way...must be the MB "engineer " in me, to do something. As stated by Fisherman,simply pulling vacuum at the shutoff valve will see if it is leaking oil. Disregard what I said about the ignition switch.
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Old 02-04-2005, 12:40 AM
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Be prepared
Oil breaks down rubber, so you may have to replace nearly everything in the vacuum system. I just had to do this and it cost around 4-500 in parts and 3 full weekends.
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Old 02-04-2005, 12:59 AM
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Location: California central coast
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Search IP shutoff, with my name, you will get lots.
Easy to do, $40. Just gotta do it right!
Brake cleaner sprayed in the lines works wonders...
be sure to let it dry b4 you reassemble.
Think Alternative Energy!
300CD '80 (now gone but not forgotten...)
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