M104 3.2 Burning Oil after Head Rebuild -- Thoughts and Guidance, please. - Page 4 - Mercedes-Benz Forum
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post #31 of 98 (permalink) Old 02-13-2017, 04:54 AM
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Originally Posted by Real1shepherd View Post
This is just all weird for a supposedly rebuilt head. I mean who would do a valve job and leave in old guides and why is the oil consumption worse now than before with the same head??

Kevin
Exactly. What else has occurred that we don't know about? What procedures did the mechanic use that we aren't aware of? Its just an endless discussion about a set of oily sparkplugs. There are very few causes of this; some more likely than others.

I am convinced there is much more to this story than what is in this thread (and that the OP isn't aware of either).

The best suggestions I can offer at this point are:
- is it possible that one of the Benzworld members in So Cal to take a look at this car to see what can be learned through a visual inspection?
- can a So Cal member recommend another Indy shop that is qualified to take over the repair of this car while maintaining some sympathy for what the owner has gone through?

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post #32 of 98 (permalink) Old 02-13-2017, 09:38 PM
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I decided to do LCG's positive air pressure test on my'89 M103 engine by opening the oil filler while the engine is idling.

I noticed that there is negative pressure (vacuum) in the valve cover.
I also decided to close the air filler and take off the valve cover breather hose from the air filter box and sure enough if I cover it with my hand vacuum develops there over time.

Is this the expected behavior? I thought the valve box would have a neutral air pressure under normal conditions.
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post #33 of 98 (permalink) Old 02-13-2017, 11:22 PM
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yeah, there's a 2 stage reed valve in the PCV that intentionally creates a vacuum if everything is working well. if you have excess ring blowby, it will cancel this and blow the oil cap off. lots of engines do this...


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post #34 of 98 (permalink) Old 02-14-2017, 04:00 AM
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So considering the results of your tests, (compression test and crankcase pressure check) the compression rings appear to be in good shape.

There is a remote possibility the oil scraper rings are causing oil to run up the cylinder passed the compression rings. This is highly unlikely since you reported all 6 cylinders have fouled plugs. Is it possible the scraper rings all failed during the month or so following the completion of the head job? I wouldn't put money on that one.

So you seem to be back to suspecting the problem resides within the cylinder head.

FYI, as far as I know the '89 M103 doesn't have a PCV valve. The crankcase is vented directly to the air filter housing through the large rubber hose. You might remove the air filter assembly and with the engine off, push the round air flow meter flap fully down so you can peer into the air flow meter casting. You would be looking for an accumulation of oil (It should be dry). Let us know what you find.

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post #35 of 98 (permalink) Old 02-14-2017, 07:51 AM Thread Starter
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Originally Posted by tuttebenne View Post
Exactly. What else has occurred that we don't know about? What procedures did the mechanic use that we aren't aware of? Its just an endless discussion about a set of oily sparkplugs. There are very few causes of this; some more likely than others.

I am convinced there is much more to this story than what is in this thread (and that the OP isn't aware of either).

The best suggestions I can offer at this point are:
- is it possible that one of the Benzworld members in So Cal to take a look at this car to see what can be learned through a visual inspection?
- can a So Cal member recommend another Indy shop that is qualified to take over the repair of this car while maintaining some sympathy for what the owner has gone through?
I am going to visit another mechanic this morning (with the car in question--something I didn't do previously). Called the dealer (in West Covina, CA) yesterday, quoted $250 for the test--which I don't have a problem with if it will give me some definitive diagnosis--but was also told once again that it will not isolate the origin of the oil burning.

There were a lot of other things that went on with this job, so I'll just tell the long-winded story from before the job until now.

1. Bought the car at 112000 miles, Aside from some occasional no-start and stalling issues, it ran very well. I had a C280 from new in 1994 as well as a 300E-2.8 from ~75000 miles in the early 2000s and the running characteristics/sound/feel were nearly identical. That's what I used as my baseline. Various relays and fuses were replaced, as well as the MAF and ECU. I also bought a used throttle actuator, but it was never put into the car. I had hoped to have that done when the head job was carried out, but the mechanic didn't feel it was a necessary thing to do. I also had some suspension work done (control arms, tie rods) but doubt this is relevant to the situation.

2. I don't really remember the exact chronology here offhand, but the head gasket started leaking around 120-130000 miles. About a pea-sized drop on the garage floor every morning. The oil loss amounted to about a quart every 2500 miles. There was no oil burning or smoke. I inquired about doing the head gasket at that time, and the mechanic advised me that the repair was unnecessary and to wait until it became more pronounced.

3. I received word that an MB shop I dealt with a long time ago was being reconstituted and since some of the family members of the proprietor are friends, I decided to give the shop a try. I did ask about sourcing my own parts prior to the job and was quoted a labor rate of $1000 for the head removal and replacement, as well as $1000 for the head rebuild plus whatever the cost would be to replace any bad valves if they were present. I think it is worthwhile to note that except the head and valve cover gaskets, all of the guides and seals I supplied were returned to me, so I presume that the machine shop declined to use these parts, which is understandable. I received a call from the mechanic stating that 7 valves were bad and needed to be replaced. I gave the authorization to proceed (it took about another two weeks just to get the head back from the machine shop). The total for this work, excluding the parts I supplied, was roughly $2900. The head was warrantied for 12 months/12000 miles. The car had roughly 135000 miles at that time.

4. Many other parts were replaced, including the water pump, wiring harness, fuel lines, heater hoses at that time. The major service was also performed and I also had some more suspension work done. The flex disc was also replaced. The cost of the entire job while the car was in the shop for more than a month, again excluding the parts I sourced, was somewhere around $4500-$5000. The strut mounts have already failed, but I take responsibility for that as I supplied those.

5. When I collected the car at the conclusion of the job, there was copious grey smoke coming from the tailpipe. I went back to the shop. The mechanic said these were residues that would burn off in time. They subsided somewhat but the smoking never went away completely.

6. After driving the car approximately 300 miles, the oil light came on. I was about 10 miles from the shop, on the freeway. I rushed to the shop to alert them of the matter. The oil was topped off and no answer was given for the rapid consumption/loss of oil. I will note that they were using synthetic 5W/30 oil which I thought was strange for this car, but the prior shop, also an MB specialist, used the same kind of oil, so I didn't question it. I may have ideas, but they are the experts. However, I became suspicious and decided to check the oil frequently. The car was burning about a quart every 400-600 miles.

7. I returned to the shop several times and the proprietor was either not present or too busy to deal with me. I relayed the problems to the workers, who relayed my messages to the proprietor. The answer I got was that the bottom end of the motor must be bad. My contention was that the car sat intact in the shop for a good week before the head was even removed, and disassembled for many weeks--was there no way to assess the bottom end and explore other options before proceeding with the head rebuild? I never received any other answer except that the top end of the motor was redone as requested.

8. The car started to develop an unsteady/hunting idle when hot after a few thousand miles, and even would die immediately upon being started. The fuel pressure regulator and starter were replaced. That problem is very intermittent but continues, and I seem to be able to overcome it by applying the throttle for about 30 seconds immediately after the car is started. The car has also started to backfire occasionally and give resistance to acceleration. I am just assuming that the catalytic converters are starting to plug up from all of the oil consumption.

For awhile I just decided to let go of the matter since I was getting nowhere, but now that 9 or 10 months have passed and I've been living with this on a daily basis with 10,000 miles on the clock, I decided that I needed to demand that the proprietor sit down with me, discuss this issue, and take the car for a couple of days to pinpoint the problem before the "warranty" runs out and we "discover" that the valves have failed. This was last week when I initiated the thread.

I will cut this short for now as I have to leave for work (and stop by this other shop on the way there) but generally speaking, however, the car still seems to run relatively well despite these problems. I'm not sure I would trust it for very long drives, but I do use it to transport large items, which is why I wanted a wagon. I drove it in excess of 100 miles on Sunday and it didn't give me any major problems, but the idle did start to hunt when the car was hot. I tried the oil cap test while the idle was hunting and oil did come out of the opening. After a few seconds, it stabilized, and nothing more came out. The cap fluttered slightly but didn't dislodge.

If it's the rings, it's the rings. Nothing I can do about that. I still wonder why this possibility wasn't brought up before starting the job to set my expectations. In other words, "just so you know, the car might burn oil after this job because your bottom end is old, do you want to continue?"

Again, I realize there are other symptoms here that may or may not be related to the oil consumption. If they are not related, I would like to focus on the oil consumption issue because this is my principal concern. I thank all of you for your input and insight with this!
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post #36 of 98 (permalink) Old 02-14-2017, 08:56 AM
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Stradivari, I do not mean to hijack your post, especially since mine is a M103 not an M104.

However, I'm hoping that my finding last night might help you as well.

Last night when I did the oil filler pressure check I reported there is vacuum there if the breather hose is plugged than a vacuum is developed in the valve cover, slowly. I though it would be positive pressure, as I thought the breather hose is there venting positive pressure to the intake, but contrary to my belief it is the opposite, it is breathing air in to the valve cover box, slowly.
Maybe this is all normal.

However, here is an oddity that involves oil burning. If I plug the breather hose and let some vacuum develop in the valve cover even for a minute or two the car starts coughing oil from the tailpipe. Very similar to the case when the car is left overnight and it coughs oil during the warm up period.

Is this not a strong sign that oil is actually getting thru the valve guides (easier with the vacuum) and into the cylinders?

If you agree is this not a test that is a straightforward test to check the valve guides that is not very invasive?
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post #37 of 98 (permalink) Old 02-14-2017, 10:23 AM
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Originally Posted by dolucasi View Post
... Last night when I did the oil filler pressure check I reported there is vacuum there if the breather hose is plugged than a vacuum is developed in the valve cover, slowly. I though it would be positive pressure, as I thought the breather hose is there venting positive pressure to the intake, but contrary to my belief it is the opposite, it is breathing air in to the valve cover box, slowly.
Maybe this is all normal. ...
On the M103 the vacuum that you detect with the breather hose opening blocked is perfectly normal.

The idle air is guided through an airduct system of itís own within the intake manifold flange, encompassing each injector. And on the M103 this air duct system is connected to the valve cover via that small rubber hose next to the breather hose. Itís actually a second breather hose, sized to a dimension suitable to the gas pressure in the crankcase during idle. It sucks in fresh filtered idle air via the main breather hose.

Btw Ö I wouldnít block the breather hose opening too often / too long while the engine is running. The vacuum thatís created inside the crankcase that way can damage the crankshaft seal rings Ö and the camshaft seal ring.

H.D.
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post #38 of 98 (permalink) Old 02-14-2017, 10:31 AM Thread Starter
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Just tried dolucasi's recommendation. Didn't sense any vacuum or blowby (nothing came out of the opening either, the cap didn't even have any tremor, and a hand placed over the opening indicated neutral pressure).

Disconnected the breather hose from the airbox with the MAF still attached and got immediate suction from the grate at the anterior end of the MAF.

The suction was immediate, so I didn't prolong anything either.
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post #39 of 98 (permalink) Old 02-14-2017, 11:34 AM
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Quote:
Originally Posted by H.D. View Post
On the M103 the vacuum that you detect with the breather hose opening blocked is perfectly normal.

The idle air is guided through an airduct system of itís own within the intake manifold flange, encompassing each injector. And on the M103 this air duct system is connected to the valve cover via that small rubber hose next to the breather hose. Itís actually a second breather hose, sized to a dimension suitable to the gas pressure in the crankcase during idle. It sucks in fresh filtered idle air via the main breather hose.

Btw Ö I wouldnít block the breather hose opening too often / too long while the engine is running. The vacuum thatís created inside the crankcase that way can damage the crankshaft seal rings Ö and the camshaft seal ring.

H.D.
Thanks for the helpful comment H.D. The question remains though, if one artificially induces some vacuum under the valve cover and the car coughs up oil, is this a sign of anything or is it a sign that valve guides are shot and in normal conditions without this vacuum, oil may still get thru the valve guides?

I only let the engine idle for a minute, no more and there was a large oil stain under the exhaust pipe.
The only other time this (oil stain under the exhaust pipe) happens with my car is during warm after an overnight cool down.
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post #40 of 98 (permalink) Old 02-14-2017, 11:36 AM
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Quote:
Originally Posted by stradivari1689 View Post
Just tried dolucasi's recommendation. Didn't sense any vacuum or blowby (nothing came out of the opening either, the cap didn't even have any tremor, and a hand placed over the opening indicated neutral pressure).

Disconnected the breather hose from the airbox with the MAF still attached and got immediate suction from the grate at the anterior end of the MAF.

The suction was immediate, so I didn't prolong anything either.
And was there any oil stain under your exhaust after this experiment?
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