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  #1  
Old 10-03-2006, 12:16 PM
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Oil pressure loss - what do you think?

Ok, this morning I had a very displeasing event.
I'm driving my 1969 220D to work, I'm about 1.5 miles from home when the oil pressure begins to drop from the normal 37 PSI down to 15 PSI. I immediately pulled over to the side of the road and left the vehicle running at idle. The pressure then began to drop even more. When I heard a slightly different that normal knocking, I quickly shut the engine off.

The oil level was about 1/2 quart low, but still in the safe range. It normally does not run that low though. So, it might have consumed some oil.

I went ahead and filled the oil back up. After restarting the engine, the pressure was normal again. I turned the vehicle around and started heading for home. When I was almost home, the pressure began to drop again. I shut the engine off and put the transmission in neutral, while coasting down a hill. Again I let the engine rest for a while, and when re-starting, had normal pressure. I made it home, but as I drove into the garage, oil pressure was below 15PSI again. And I noticed a different knocking sound.

Again, I let the engine rest. Upon re-starting, the pressure was above 15, but not at 37. I reved the engine up a few times and it sounded normal.

I don't intend to drive the vehicle again until the problem is resolved.

I am struggling with what could be the cuase . My first suspision is that the oil pump is going bad, or the oil pump intake screen is clogged (might explain why letting it sit allows normal oil pressure).

I don't think that I damaged the engine in any way (I hope).

There was more black smoke than normal when the oil pressure would drop. Is this an indicator of bad valve timing?

Any feedback is appreciated.

I can't hardly think about work, cause my mind is on my poor little mercedes sitting at home. It's driving me crazy


Last edited by Newguy; 10-03-2006 at 01:47 PM.
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  #2  
Old 10-03-2006, 12:54 PM
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It does sound like an issue maybe with the oil pump, and the symptoms would be consistant with a blocked screen. Should not cause a difference in smoke though. Do those cars have an oil cooler?
Ummm, btw, quit revving it with low oil pressure.....
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Old 10-03-2006, 01:43 PM
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Yes it does have an oil cooler.

I guess my 1st step will be to drop the oil pan and take a good look at sludge / debris. Also hope that I don't see any metal shavings.

I will probably replace the oil pump while I am in there.
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  #4  
Old 10-03-2006, 01:55 PM
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I drove a little W123 240D a few weeks ago, and it also had very low oil pressure. Had the correct oil level. After a test drive of 5 miles or so, I came back due to the low oil pressure. The oil cooler was cool to the touch, so it appeared there was no oil "flow". He said he would have his mechanic check the pan, but they sold it that afternoon. He said he hadn't driven the car much, but the oil hadn't been changed in a couple of years. I assumed sludge.
I hope the buyer notices that..........

Your approach sounds correct. You might snap us a picture when you take the pan off. I would like to see that oil pump situation....
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Jimmy L.
'05 Acura TL 6MT
2001 ML430 My Spare

Gone:
'95 E300 188K "Batmobile" Texas Unfriendly Black
'85 300TD 235K "The Wagon" Texas Friendly White
'80 240D 154K "China" Scar engine installed
'81 300TD 240K "Smash"
'80 240D 230K "The Squash"
'81 240D 293K"Scar" Rear ended harder than Elton John
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  #5  
Old 10-03-2006, 02:05 PM
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Interesting development

I am actually having difficulty finding a replacement oil pump.
This web site, and 2 others don't even show an oil pump part #.

I guess I'll keep looking.
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  #6  
Old 10-03-2006, 04:18 PM
david s poole
 
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while the pan is off take down #2 rod bearing and have a look.it might be that the bearings are worn and as the oil heats up[and bearings too]the clearances get bigger allowing the pressure to drop.
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Old 10-04-2006, 11:59 AM
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Good and bad

Well, I've got sum good and bad news.

Good news - I fixed the oil pump issue. There is one single bolt that holds the oil pump up to the bottom of the engine. This one bolt had sheared off somehow, and chunks of it were lying in the oil pan.
As you might imagine, this allowed the oil pump to drop a little bit, which did two things.
1) The key which turns the pump was barely in contact, and chewed up the end of the key. Thats not so bad, cuz with a little deburring it fit quite well back into the keyway.
2) The oil pump came to rest on the inside of the oil pan. This acted as a nice seal and prevented oil from entering the oil pump. Thus the low pressure.

Bad news - I have quite a bit of bearing shavings in the oil pan

So, I figured I would put it back together and have a listen.

It don't sound so good no more. Oil pressure is up though.

I've never torn into a mercedes engine - as far as rebuilding, does anyone know how difficult it can be as compared to american engines?

I know that to purchase a rebuilt engine is quite spendy.

I could always look for a donor car.

Anybody have any Ideas? I am really sad at this piont.
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Old 10-04-2006, 12:41 PM
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If you have the time, tools and place too work, rebuilding the 616 is a pleasure. What I did was take my time and rebuild a "parts car' engine and then swap it in over a week end. No down time and no rush. I spent close to 3K but that included new over size pistons, liners...lots of new parts including radiator, clutch, p/p, starter motor. It was so much fun, i did another the following year
Lots of things to consider, hows the rest of the car? Do you like to wrench? If you've ever configured a VCR you could proly rebuild one of these engines
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  #9  
Old 10-04-2006, 01:27 PM
david s poole
 
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glad you found your problem,now the good news.you can prob replace all the bearings on the crankshaft[pull one of each and you will find the size and part # on the back]with the same ones assuming that the crankshaft has not been damaged.remove complete oilpan[off with fan shroud ,both motor mounts and disconnect some wiring] and jack car up.if you take your time you can polish up the crank with narrow emery [fine] cloth.pay attention to torque specs when fitting new bearings.
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European Performance
Dallas, TX
4696880422

"Fortune favors the prepared mind"
1987 Mercedes Benz 420SEL
1988 Mercedes Benz 300TE (With new evaporator)
2000 Mercedes Benz C280
http://www.w108.org/gallery/albums/A...1159.thumb.jpg
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  #10  
Old 10-04-2006, 01:47 PM
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You think most of the damage is the main bearings?
So, probably nothing up top got damaged?

If that's the case, I could have the main bearings replaced pretty quickly.
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  #11  
Old 10-04-2006, 03:16 PM
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pull the VC and have a look at the camshaft.

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