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  #1  
Old 06-09-2014, 02:30 PM
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Crankcase Pressure

Hey all,

My 81 300SD seems to have high pressure coming from the crankcase. I recently replaced the turbo and rebuilt the injectors with new Monark nozzles. I am getting a lot of smoke coming from the valve cover.

My compression test results were around 380 PSI. Cylinder 5 was pretty low, but I let the cylinder soak in MMO for a few weeks and the compression is now up to 400 PSI.

I did the dancing cap test and it doesn't seem to dance too bad. The dancing completely stops as I increase the RPMs. There is a lot less smoke coming from the tailpipe now that I've rebuilt the turbo and injectors, but the blow by seemed to remain the same. I can see smoke coming from the oil dipstick, but it does not come loose while driving. I could be wrong, but it seems that the pressure from the valve cover is pushing up the fitting that connects the valve cover hose to the air cleaner. Even after buying another valve cover from a member of this forum, it still seems to leak oil from the nuts on the valve cover, and I'm thinking this is due to pressure in the valve cover...??

I have been doing some research and it seems that cleaning the oil separator may do the trick. Does anyone else have any ideas as to what may be causing this? I do not think the rings are the cause since I received good compression test results across the board. My vacuum system seems to be working fine as well (car shuts down instantly, all locks work), so I'm not sure that this would be the issue either.

Thanks!

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  #2  
Old 06-09-2014, 06:08 PM
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You can have compression rings that are still great but the oil control rings can be marginal.

You soaked one cylinder because it was low in compression. Then it went normal. Did you soak all the other cylinders? My thoughts are if one was stuck chances are some of the others may be partially so ring wise.

If not I would do that. The soaking again obviously loosened up something that was stuck. If the car has been on vegetable oil specially make sure they all get a good soaking. Probably about the cheapest thing you can do with some potential upside.

Sometimes the rings stick a little just from siting around. A container of miracle mystery oil added the the base oil of the engine will do no harm either in my opinion. It seems to be a powerful solvent.
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  #3  
Old 06-09-2014, 08:09 PM
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I only soaked cylinders 3 and 5 in the MMO since I had to remove those injectors again. 3 actually seemed lower from what I remember. Not sure why... it has never been run on VO. I'm thinking maybe valve guide seals? I really want to figure this out soon! I've only driven maybe 15 miles since I replaced the turbo and injectors, so I'm hoping maybe once I get it on the highway it will run smoother and burn up any residual oil that's been left over. The car sat for 8 years without being run, and since I've been working on it sporadically I've only put about 100 miles on since then.

Any other input is appreciated.

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1981 Mercedes 300SD - 186k miles

1978 Corvette Pace Car - 21k miles

2006 Mazdaspeed 6 - 56k miles
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  #4  
Old 06-10-2014, 01:10 AM
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I'd be doing a leak down test at this stage (this doesn't help if you don't have access to a compressor though)
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1992 W201 190E 1.8 171,000 km - Daily driver
1981 W123 300D ~ 100,000 miles / 160,000 km - project car stripped to the bone
1965 Land Rover Series 2a Station Wagon CIS recovery therapy!
1961 Volvo PV544 Bare metal rat rod-ish thing

I'm here to chat about cars and to help others - I'm not here "to always be right" like an internet warrior



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  #5  
Old 06-10-2014, 03:03 AM
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It is always bad news when you have smoke coming from the dip stick hole or the valve cover. I do not know whether there is a vent hole on the left back corner of the valve cover in the 617 engine. There is one in the 60x engine. If there was and you see smoke coming out from there then the engine blow-by is bad, very bad.

I doubt MMO frees the coked rings and increases your compression to 400PSI. I suspect the oil soaked the gap and you are doing a 'wet' compression test so to speak. It will give misleading readings. You need to wait for all the MMO to drain and redo the test again. Or do a leak down test.
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  #6  
Old 06-10-2014, 08:51 AM
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How many miles on the engine ?
It does not sound like you have driven it enough to know if it is burning crankcase oil.

Quote:
Originally Posted by 300SD90 View Post
...it seems that the pressure from the valve cover is pushing up the fitting that connects the valve cover hose to the air cleaner. ...
I have been doing some research and it seems that cleaning the oil separator may do the trick.
Clean your oil separator and make sure the tube is not blocked. See if that has fixed the problem.

Quote:
Originally Posted by 300SD90 View Post
... The car sat for 8 years without being run,.... I've only put about 100 miles on since then.
People usually do not park a good running car for 8 years for no reason. Why was it parked ?

If it runs and drives and holds is vital fluids ok, then take it out for a drive. Get it warmed up. Find a long hill and push it a little bit, several times.

Do a dry compression test, then a wet compression test (add a teaspoon of oil to the cylinder just before testing it).
If the dry test shows a low compression cylinder and the wet test shows significant improvement, then the rings are worn or stuck.
If the low cylinder does not improve, then the leak is through the valves. In that case, adjust your valves.

I have had good results loosening stuck rings with water injection.
I have had good results fixing worn rings by... replacing them.
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2012 S350 BlueTEC 4Matic
2007 ML 320 CDI
2007 Leisure Travel Serenity
2006 Sprinter 432k
2005 E320 CDI
1998 SLK230 (teal)
1998 SLK230 (silver)
1996 E300D 99k, 30k on WVO
Previous:
1983 240D, on WVO
1982 300D, on WVO
1983 300CD, on WVO
1986 300SDL 237k, 25k on WVO (Deerslayer)
1991 350SDL 249k, 56k on WVO - Retired to a car spa in Phoenix
1983 380 SEC w/603 diesel, 8k on WVO
1996 E300D 351k, 177k on WVO

2007 ML320 CDI .. / 2005 E320 CDI .../ 1998 SLK 230 .../ 1991 Daihatsu Rocky
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  #7  
Old 06-10-2014, 10:09 AM
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Sitting eight years is quite a time. May improve with some milage I agree. The reheating and cooling down with the differential of expansion and contraction being repeated may help as well. The rings are cast iron and steel. The pistons are normally aluminium.

Again I would add a quart of miracle mystery oil to the base oil. It may do nothing on the other hand It will not hurt.
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  #8  
Old 06-10-2014, 11:17 AM
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If you really want to clean up your engine, run synthetic oil in it.
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  #9  
Old 06-10-2014, 11:18 AM
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The compression test results were all 350+. I soaked two of the cylinders in MMO, and before running those tests again I ran the engine to operating temp and then took the compression test, which seemed to improve cylinder 5 which was at 280 PSI previously. Because the dry test went well, I did not do a wet compression test.

Quote:
How many miles on the engine ?
It does not sound like you have driven it enough to know if it is burning crankcase oil.
The car has 186,000 miles. Like I said, I am also hoping that it just needs to be driven. I've put roughly 100 miles on the car so I don't think that's enough, and most of that is city driving.

Quote:
People usually do not park a good running car for 8 years for no reason. Why was it parked ?
It was my uncle's car. When he purchased a new car, he put the 300SD on jacks in his garage and left it there for 8 years, until he decided it was time to get rid of it which is where I came in! He said it was running great when he had it, but I can't really trust that he knew what a great running 300SD is really like.

Quote:
Again I would add a quart of miracle mystery oil to the base oil. It may do nothing on the other hand It will not hurt.
Has anyone done this with positive results? I have never heard of putting MMO mixed with engine oil, but I'm definitely going to look into doing this because I've heard of many benefits that come from using MMO.
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  #10  
Old 06-10-2014, 11:36 AM
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yes I have freed stuck lifters.Sounds like rings are stuck,and running with MMO for a few months should help.;
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  #11  
Old 06-10-2014, 11:49 AM
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Quote:
Originally Posted by oldsinner111 View Post
yes I have freed stuck lifters.Sounds like rings are stuck,and running with MMO for a few months should help.;
What ratio or percentage of MMO to oil would you recommend to free stuck rings? 10W40 is pretty thick, so I'm not too worried about the MMO thinning out the oil, which can cause major problems obviously. I may put in half a quart...?
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1978 Corvette Pace Car - 21k miles

2006 Mazdaspeed 6 - 56k miles

Last edited by 300SD90; 06-10-2014 at 12:02 PM.
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  #12  
Old 06-10-2014, 12:07 PM
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I'll (quietly) point out that you are making an assumption that the problem is the rings and hope this helps
__________________
1992 W201 190E 1.8 171,000 km - Daily driver
1981 W123 300D ~ 100,000 miles / 160,000 km - project car stripped to the bone
1965 Land Rover Series 2a Station Wagon CIS recovery therapy!
1961 Volvo PV544 Bare metal rat rod-ish thing

I'm here to chat about cars and to help others - I'm not here "to always be right" like an internet warrior



Don't leave that there - I'll take it to bits!
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  #13  
Old 06-10-2014, 12:54 PM
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Quote:
Originally Posted by Stretch View Post
I'll (quietly) point out that you are making an assumption that the problem is the rings and hope this helps
X2

Have you confirmed that the CCV system is in working condition yet ?
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Greg
2012 S350 BlueTEC 4Matic
2007 ML 320 CDI
2007 Leisure Travel Serenity
2006 Sprinter 432k
2005 E320 CDI
1998 SLK230 (teal)
1998 SLK230 (silver)
1996 E300D 99k, 30k on WVO
Previous:
1983 240D, on WVO
1982 300D, on WVO
1983 300CD, on WVO
1986 300SDL 237k, 25k on WVO (Deerslayer)
1991 350SDL 249k, 56k on WVO - Retired to a car spa in Phoenix
1983 380 SEC w/603 diesel, 8k on WVO
1996 E300D 351k, 177k on WVO

2007 ML320 CDI .. / 2005 E320 CDI .../ 1998 SLK 230 .../ 1991 Daihatsu Rocky
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  #14  
Old 06-10-2014, 02:06 PM
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Just to clarify, I won't be adding MMO to the oil until I've exhausted all other possibilities. I just wanted to know for future reference. I honestly do not think the problem is the rings, so I am trying to check everything else first.

Is there a thread on how to test the CCV system? So to answer your question, no I have not.
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1978 Corvette Pace Car - 21k miles

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  #15  
Old 06-10-2014, 08:49 PM
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The 81 300SD Crankcase Ventilation System is a Valve Cover with some baffles in it and a hole in the Valve cover with tubing that I think in your case goes directly into the Air Inlet before the Turbo.

On My 84 W123 the Crankcase Vent Tube is routed into the Air Filter Housing throuh a Breather that is supposed to seperate the Oil from the Vapor and the Vapor goes into the Air inlet.

So as long as all the that is open there is nothing to the Crankcase Vent System.

On My year and Model is not uncommon for these Engines to have enough Blowby that the Breather/Oil Seperator in the Air Filter Housing cannot do the job and Oil can get on the Air Filter Element.
And mine was doing that exact thing.

If soaking the Cylinders in something will not help the Blowby; and I tried that on mine and it did not work you just have to live with the Blowby till such time as you wish to go through the Expense to overhaul the Engine.

Blowby can also come from worn out Valve Stems and Guids in the Cylinder Head and I think also from worn out Valve Stem Seals. I changed the Valve Stem Seals on mine and if it helped I could not tell.

How much is too much Blowby.
If your Engine Seals are reasonably good and you get enough Blowby the Crankcase Pressure will act on your Vacuum Shut off and push it into the Shutoff position messing with your idle.
Some People have had the Crankcase Pressure increase their Oil leaks.

I am not recommending that you do this but at hot idle if I block off the Crankcase Vent in the Valve cover in about 7 seconds My Engine starts to stumble on the way to shutting off.

If your Oil Fill Cap is not dancing around when it sits there loose your Blowbay is not at all bad.

Please note that someone testing blocked off their Crancase Vent and did that too long and the Front Crankshaft Seal popped out.

I have the Factory Service Manual CD Set and the actual Books and I have not ever seen a Crankcase Pressure Test in the Manual. But, I admit I have not specifrically looked for that.

Stretch has the German Version of that Manual and claims there is whole bunch of stuff in that Manual that is not in the USA Version. So you might PM him and ask.

Just for kicks.
If I remember correctly on other Engines you connect a Water Manometer to someplace that is exposed to the Crankcase Pressure and use that to measure it with. A Manometer is a U shaped Tube with long legs on the U and on each side there is an inch or metric ruler. Water is poured inside of the Tube and when you start off the Water is level on got sides.
The measuerment would be in inches of Water

You connect one side to the pressure and that pushes the Colum of Water up the other side and and you use that side to measure. The Measuerment would be in inches of Mecury.

To check Exhaust Back Pressure the U Tube would be filled withe Mecury.

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