Oil on the hood...blow by? - Mercedes-Benz Forum

 
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post #1 of 8 (permalink) Old 10-09-2011, 05:51 PM Thread Starter
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Oil on the hood...blow by?

I bought this 1979 240d over the summer from a man who used it as a daily driver. I commuted every other week in it about 30 miles round trip/day with no problems whatsoever, didn't even smoke. The vehicle continues to run very well (albeit slowwww!).

I started noticing small streaks of a dark black substance creeping up the hood a few weeks ago. I popped the hood saw that there was a decent amount of residual oil at the air intake hose/tube over the passenger head light, not pooling, but like soot, covering lots of that front passenger side near the headlights. I cleaned it up, checked the air filter housing - and while there as a sooty covering of oil around the inside, there was no standing oil (I don't have the oil bath type of filter). I also was low by about 2 quarts of oil so I topped it off as well.

After the next freeway drive the same thing happened, oil on the hood. I have resorted to placing paper hand towels around the air intake opening to prevent the oil from creeping out. The car progressively began to smoke more and more whitish smoke when starting and sitting at lights.

Is this excessive blow by? Air filter replacement? I noticed the previous owner had clipped and sealed off a hose attachment on the top of the air filter housing (the only one there, other than that which goes to the valve cover) is this a problem? Many thanks!

(I have been searching on this topic for weeks now and have not heard of another case like this)
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post #2 of 8 (permalink) Old 10-10-2011, 04:49 PM
KCM
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Concerning the line sealed at the top of the air cleaner, does it run to the front of the engine and connect to a unit at the front. If so (and I'm pretty sure it does), that is the vent line for the vacuum pump (the unit on the front of the engine). This line should not be plugged for the vacuum pump to work properly. Does the vacuum system and brake booster work properly? If not, then the vacuum pump probably has a torn diaphragm which would pump oil into the air cleaner, and the reason the previous owner blocked the line.

As for the oil at the air cleaner inlet, I am surprised there was no oil pooled in the air cleaner. Not sure how oil would get way out to the headlight without a lot of oil in the air cleaner. Plus I think the breather line is on the engine side of the air cleaner rather than the air intake side (??? I might be wrong), so don't know how oil would get out that far. If the breather line is on the intake side of the air cleaner, than that and blow-by would definitely cause the oil you see. You can check for blow-by by disconnecting the hose at the top of the valve cover. If it smokes like a locomotive, you definitely have blow-by. A little smoke does not mean the engine is shot. You also said you had to add 2 qts of oil. After how many miles? That does sound like a lot, but depends after how long. Might very well be a very worn engine.

If you can post a picture or two of the air cleaner area, that might help to diagnose the problem. There might have been some rework done of that area by the previous owner that is causing you problems.
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post #3 of 8 (permalink) Old 10-10-2011, 08:05 PM Thread Starter
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KCM

Thanks for the input. I took some pictures this evening illustrating what is going on. In response to your questions: The hose on top of the air filter housing does appear to be what you described (pic) - probably goes to the vacuum pump, however, I don't notice any problems with the brakes or vac. If the little orange brake light comes on at the dash would that indicate a problem with the booster? Mine flickers on and off when I apply the brakes once in awhile. I was thinking it was that the pads were getting worn. Might be onto something there...

I checked for blow-by as you described - not much there, just a bit of black oil/soot that deposited on my finger, but no smoking. I only had time to partially warm it up so I will check again after freeway driving.

Thanks for all the help and I appreciate any more input.

This one is of the intake.


This is the hose on top of the air filter housing.


Inside the air filter housing - no pooling of oil.


Hood/front where oil/soot is coming out onto the hood.


Paper towels that soaked up the oil after about 50 miles.
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post #4 of 8 (permalink) Old 10-11-2011, 06:47 AM
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Can you take a picture of the breather hose on top of the valve cover? Especially where it connects to the intake manifold. If that hose is connected before the air filter, oil could come out of the air intake.
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post #5 of 8 (permalink) Old 10-11-2011, 10:09 AM
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Another thought on the blocked line on top of the air cleaner. Being as I don't see any other line there, it is possible that the vacuum pump was retrofitted from the original diaphragm style to the new piston style. I believe the piston style vents into the engine rather than to the air cleaner, so does not use that port on the air clener. The piston style would only have one line connected to it rather than two.

Not sure about the oil yet. Something has to be pumping that oil in there for it to come out. Vapor should be sucked into the air filter and engine, not out the inlet.
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post #6 of 8 (permalink) Old 10-11-2011, 12:04 PM
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It could be that a newer intake manifold has been installed (or an engine of a later date) with the EGR valve stuck open. The pressure from the exhaust gases could divert the vapours.

If the oil went through the air filter, the filter would be drenched. If the breather hose is connected before the filter, I suppose oil could drip out of the tube too.
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post #7 of 8 (permalink) Old 10-11-2011, 07:54 PM Thread Starter
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KCM

I did the test as you described earlier today. I removed the breather hose from the valve cover after a healthy 20 min. freeway drive. There was only minimal blow-by/smoke evident, even when revving the engine - definitely present, but not "smoking like a locomotive". A few specks of oil were deposited on my finger that I held in front of it after about 5 seconds - didn't seem too worrisome. Also, the oil filter is mysteriously not drenched - this must be what you were eluding to with finding out where the breather from the valve cover connects to...

Govert

Below is an image that shows the breather hose at the valve cover, I did not have a chance to get a shot of where it connects to the intake yet so I will do that tomorrow (have to pull off the air filter housing). I found the other image with the red circle near the vacuum lines on the driver side of the vehicle and was wondering if that is where the plugged hose on top of the air filter housing is supposed to go...?


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post #8 of 8 (permalink) Old 10-12-2011, 05:19 AM
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The plugged line on top of the air filter housing is for the membrane-vacuum pump. If it is plugged, it could not cause the oil spillage. As KCM said, if the pump has been replaced by a newer piston pump, the hole should be plugged.

The open line on top of the injection pump is part of the so-called ADA. It should be open to outside air pressure, so that if you drive in the mountains, where less air is available, less diesel is injected to prevent smoking.

The breather hose usually sprays a bit of oil with the fumes straight into the intake manifold, below the air filter. Normally the oil will not creep upwards, not in any significant manner, because of the air flow. It can happen when there is a lot of blow-by fumes and/or an EGR valve which is not functioning properly. The bottom of the air filter will be oily or even drenched in oil if it is a lot.

It is also possible that if the valve clearance isn't adjusted properly and that an intake valve is (partly) open during the compression stage. That will push out air and disrupt the air flow. Have the valves been adjusted any time lately?

My advice would be to take off the air filter housing and inspect the breather hose connection and possibly an EGR valve. The last thing is only possible if the intake manifold or engine has been changed, because EGR came only from 1980 onwards.

Inspect and adjust the valve clearance too if you haven't done that.
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