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Car Forum / Mercedes-Benz Cars / February 2008240 D blow by / oil usage.
I have a 240 D with high oil usage that diminishes with the oil level (as splash lube decreases, crank air dries out). Lack of an obvious leak on the valve cover or head gasket, and the uniform coating of oil under the hood make it look like blow by but I got some conflicting information. Ring blow by seems negligible based on the valve cover breather test per: http://www.frybrid.com/forum/showthread.php?t=301 I can block the breather at a warm idle and engine speed does not change at all over 10 seconds. An oily blows out of the breather tube. Crankcase vacuum as measured at the oil filler tube was 10-20 mm Hg at about 1/2 throttle- hard to tell as it was as full scale is 760 mm Hg. Manifold vacuum was 60-80 mm Hg at about 1/2 throttle. So I'm confused, I thought I'd find high manifold vacuum drawing excessive air through the crankcase or something. Do I just need to replace the breather? And if so, where do I find one, tried autozone and autohausaz, no luv. What does this information say about the health of the engine as well. Thanks, Andy Generally, blow-by indicates the piston rings are no longer holding compression - its "blowing by" (the rings) into the crankcase. Usually such motors burn oil and get hard to start, especially in cold weather. Blow-by doesn't mess up the engine space, leaks do. If everything is oil covered I suspect the motor's front crankshaft seal is leaking and that oil is being blown all over the motor and engine space. But you want to replace the breather - the hose from the valve cover to the intake manifold (to dispose of the fumes). www.PerformanceProducts.com sells the rubber 90 degree "breather hose" that attaches to the valve cover p/n 01-028 for $7.05 (Page 150 of their free paper Catalog 55M) Another possibility is a significant vacuum leak in the car or brake booster. The later years use a vacuum pump that dumps its output air into the motor so a vacuum leak adds to the crankcase air volume. © 2007 T.G.Lambach. Publication in any form requires prior written permission. On Dec 8, 5:40 pm, "-->> T.G. Lambach <<--" <"T.G. Lambach at NoHamorSpamcomcast.net"> wrote: > Generally, blow-by indicates the piston rings are no longer holding > compression - its "blowing by" (the rings) into the crankcase. Usually [quoted text clipped - 15 lines] > (c) 2007 T.G.Lambach. Publication in any form requires prior written > permission. Ohhh, thought the breather had a PCV valve. No, plumbings all set. TG, you mentioned the vacuum leak before, but now I get it. An 82 should have the pump I does seem to leak some vacuum- the power locks never work, and when i pull it out of the driveway and turn it off the brake pedal is hard and it runs on till I stop it w/ the clutch. I only see this before I drive it so I assume it's accumulating vacuum and leaking it off overnite. I trust I can decay test each system w/ a vacuum pump and go from there.Still, the additional flow should just be looped & burnt if it goes to intake manifold. Motor starts easy, it's been 20 F +/- glow plugs, crank a few revs, touch the accelerator if you need to, hold a little pedal till it stabilizes. Can you get at the crankshaft seal just by moving the fan, radiator and timing chain cover? OK, OK, Stop. The more you describe this car the more I believe the motor is fine but is laboring from other, non-diesel, problems. Forget about the front seal. Find and fix the car's vacuum leak(s). You can't drive a car with non-power brakes. There are vacuum check valves to precisely prevent what you experience. There's the power brake and a small line to the "comfort system" for the heater and door locks. Leak could be inside the brake booster or the vacuum reservoir or ????. One way is to plug the various systems and see when it's better. If vacuum pump itself is weak, no worry, these pumps can be self rebuilt with a $40 repair kit if that's necessary. Fixing this will take some time and patience suggest you start with a vacuum diagram so you know how it should be working.  Signature© 2007 T.G.Lambach. Publication in any form requires prior written permission. On Dec 8, 8:30 pm, "-->> T.G. Lambach <<--" <"T.G. Lambach at NoHamorSpamcomcast.net"> wrote: > OK, OK, Stop. > [quoted text clipped - 20 lines] > (c) 2007 T.G.Lambach. Publication in any form requires prior written > permission. Will take a look. I think the vent to cabin is already blocked off. What vacuum should the pump produce, and what should the system hold? I've got a 1 bar full scale vacuum gage. My 1978-80 300SD Manual tests the vacuum pump suction at a connection point between the brake booster and its vacuum check valve. Vacuum at that point should be between 700 and 800 millibar 20.67 and 23.63" of Hg after running the motor for a few minutes at idle. I don't know the system's vacuum reserve capacity. If your car's "comfort circuit" is disconnected, is its port on the vacuum pump plugged? If not that may be the problem. Signature© 2007 T.G.Lambach. Publication in any form requires prior written permission. On Dec 9, 11:13 am, "-->> T.G. Lambach <<--" <"T.G. Lambach at NoHamorSpamcomcast.net"> wrote: > My 1978-80 300SD Manual tests the vacuum pump suction at a connection > point between the brake booster and its vacuum check valve. Vacuum at [quoted text clipped - 7 lines] > (c) 2007 T.G.Lambach. Publication in any form requires prior written > permission. Thanks. I can see oil in the manifold, and cleaned a bunch out of the filter plenum, but how's it cross the filter, or otherwise get into the engine compartment? A piece of paper over the intake made it look like theres no overlap on the cylinder intake cycles, and thus no rebounding flow out the intake. Also, what's a good service manual for the 82 240D. I'm not suprised that chiltons is lite on the details, but the benz 123 CD is super in some spots, like wiring schematics, and not there at all for references to the cars vacuum system? The manuals to buy are the old M-B paper ones that are occasionally sold on e-bay.com. There's a 123 chassis manual that covers the car in detail but not the motor or transmission. Chilton tries to cover too many models, leads the reader down the path to a repair and then stops, leaving the reader hanging out to dry. The other alternative is to pay an independent M-B shop to figure it out. Signature© 2007 T.G.Lambach. Publication in any form requires prior written permission. Also see: http://www.tmcpubl.com//mercedes.html and www.books4cars.com Signature© 2007 T.G.Lambach. Publication in any form requires prior written permission. > My 1978-80 300SD Manual tests the vacuum pump suction at a connection > point between the brake booster and its vacuum check valve. I tried to disconnect the valve from the hard plastic lines and couldn't get anything to move. Any recommendations on how to pop this check valve out short of using a knife to cut the lines? thx- -tom! -- I assume my 84 190D (OM601 engine) also has blow-by. It has 253k miles now, quite noisy and oil leaking out from the new oil cap and valve cover gasket. However, one thing I don't understand is, the start is very easy. After the glow plug light is off, the start is instantaneous, not even taking one full second to crank. I thought blow-by means lower compression (yes, its compression is in the low margin). So why is it so easy to start? > Generally, blow-by indicates the piston rings are no longer holding > compression - its "blowing by" (the rings) into the crankcase. Usually [quoted text clipped - 4 lines] > © 2007 T.G.Lambach. Publication in any form requires prior written > permission. Blow-by is a result of lower compression and so a symptom of same. As to why your motor starts easily.... good glow plugs, thin oil, good battery, good starter etc. At some point the compression will be insufficient to ensure quick starts. Frequent oil changes, say 3K miles, will postpone that sad day. Does it burn oil? In "moon"'s case, his 240D starts well, like your engine, so I suspect his motor's vacuum pump is blasting air into the crankcase and blowing oil out the breather. I believe his 240D has a vacuum leak somewhere which is the real culprit of the motor's oil loss. Signature© 2007 T.G.Lambach. Publication in any form requires prior written permission. I can't say for sure if it burns oil, unless I capture all the leaking oil and measure it :-) There is never blue smoke though. The oil goes down a quart every 3000 miles. I consider the oil leak as heavy, though not yet serious. Most leak is from oil cap and valve cover gasket (both new). Some leak from head gasket (around cylinder #1 & 2). > Blow-by is a result of lower compression and so a symptom of same. As to > why your motor starts easily.... good glow plugs, thin oil, good [quoted text clipped - 9 lines] > oil out the breather. I believe his 240D has a vacuum leak somewhere > which is the real culprit of the motor's oil loss. One quart consumption every 3000 miles is absolutely normal. They never covered "dealing with the obvious" in engineering school--- damn perfessers! Plugged the cabin vacuum line back into the T, now idle, brakes, throttle response & shutdown are much better. If there's any more oil use, it'll have to be a seal somewhere. Thanks TG. On Dec 10, 11:23 am, "-->> T.G. Lambach <<--" <"T.G. Lambach at NoHamorSpamcomcast.net"> wrote: > Blow-by is a result of lower compression and so a symptom of same. As to > why your motor starts easily.... good glow plugs, thin oil, good [quoted text clipped - 12 lines] > (c) 2007 T.G.Lambach. Publication in any form requires prior written > permission. A follow up on the blow-by/low compression. I guess my 190D's low compression is proved today. It was 15 Fahrenheit this morning. The engine cranked but took several tries to start. It ran rough for about 15 seconds. Tom is right. That sad day may not be too far away. > Blow-by is a result of lower compression and so a symptom of same. As to > why your motor starts easily.... good glow plugs, thin oil, good [quoted text clipped - 9 lines] > oil out the breather. I believe his 240D has a vacuum leak somewhere > which is the real culprit of the motor's oil loss. Wan-ning Tan schrieb: > I assume my 84 190D (OM601 engine) also has blow-by. It has 253k miles > now, quite noisy and oil leaking out from the new oil cap and valve [quoted text clipped - 3 lines] > blow-by means lower compression (yes, its compression is in the low > margin). So why is it so easy to start? There are three oe four piston rings, the upper two making the compression, the lower ones are scratching most of the oil from the wall going down. If the oil rings are sittking clogged you have nice compression but you burn rests of oil at the wall at each stroke. The main other oil leak to combustion chamber are the valve gaskets but thats not so much of a problem for diesels. The sucking vacuum at open intake valves is small compared to a gas engine running at closed throttle. SignatureRoland Franzius |
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