One thing missing from Brian's equation, is the oil that gets on top of the piston, past the oil ring, and is burned. Blow-by is only a measure of what the cylinder loss is in one direction. Also, with blow-by, there is some oil lost to vapor, that must be condensed out of the hot air, before it can be measured. The " smoke from under the hood" would qualify as oil smoke. A decent "test" nonetheless.

so the oil that gets by the rings is coming from the oiling slots on the piston right? this may seem strange coming from me but i have never talked about it before. so that is the source of blue smoke on any car that is smoking from wear, right?

and if it is not worn, the oil from the oiling slots is simply swept back into the pan, right?

tom w

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[SIGPIC] Diesel loving autocrossing grandpa Architect. 08 Dodge 3/4 ton with Cummins & six speed; I have had about 35 benzes. I have a 39 Studebaker Coupe Express pickup in which I have had installed a 617 turbo and a five speed manual.[SIGPIC]

..I also have a 427 Cobra replica with an aluminum chassis.

Don't forget to consider valve seals.

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'82 300SD - 361K mi - "Blue"

"Good judgement comes from experience. Experience comes from bad judgement."

listen, look, .........and duck.

Very likely the most over looked part of the oil consumption problem with these old diesels. The valve guides will wear out almost to an oval in time, that can be limited with frequent oil changes, but how can you know the cars history to that degree when it is bought used?
I had the head rebuilt on mine last summer, the old guides were well worn. New guides and a fresh set of seals cut the oil consumption by 2/3's. far less smoke out the backside.

Thanks Brian,a lot of tests are not absolute but many provide indications. Anyone designing them for consideration is very much appreciated. Far better than nothing or just absolute guesswork as an alternative. Plus sometimes they can be refined into useful comparisons. This test for example screams for baseline information from other engines. The engine does create some small vacccum component. I believe or it would be unable to suck air and blowby through the air filter when pipe is connected to the filter housing. When pipe was just directed to container even that small component was gone although perhaps not too signifigant or perhaps it is. . But totally diluted by the vent pipe termination outside the filter housing. The same test made by construction of a real oil trap installed on that line might or might not give a better indication. Should though I imagine. I surmise the seals in the turbo are still suspect though. Certainly not ruled out. Could easily be a combination fault of various problems making an overall contribution. Sad their is no existing refferences until a few more try it and we get a guildline going? Have to wonder if any amount of oil would be collected from one of my engines?

You can have good compression rings and poor oil ring function at the same time. The poor oil rings will just not scape the oil off the walls and it lands up being burnt. Or it is just going by them at a greater rate than design. Or even worst the excess clearance in the piston lands enables them to become minature oil pumps. At a thousand miles per quart you just might notice a difference in tailpipe emissions if oil is being burnt primarily. But I suspect not very much and you would have had to own the same engine in better condition to even risk an evaluation based on that. At 200-400 miles per quart the emissions become pretty obvious. your consumption rate appears to be increasing pretty fast. One might consider driving it for a time just adding oil until it is more clear cut. That is if engine is starting and running reliable right now. Another quick and good test in your hot part of the country is to change oil to a straight 40 weight or 50 weight oil. Perhaps a gallon of each if it makes you feel better. If oil consumption drops in half it probably is the engine rather than turbo bearing related. Pete is also right the seals could be making a contribution as this engine has had one ring job already and if they did not touch the head those seals might be getting tired as well. Again this might be a problem partially caused from a little deficiency here and there. Using a thicker base oil will define it somewhat as a diagnostic tool. A straight 40 or 50 weight has so much more viscosity than a multi grade oil in actual service it is almost unbelievable. Really helps seal thing partially up. If blowby drops way way down you pretty well have your answer. If nothing else it should rule out or condem the turbo seals as a major contributor in my opinion. If it is the turbo seal I would expect only a slight reduction in consumption with the heavier oil. If it is the engine I would expect a doubling of miles per quart burn ratio perhaps even more. Post some information down the road for everyones benifit. There is another test as well come to think of it. When turbo is cold take off ductwork and feel for excess play in bearings. Not conclusive but really worn bearings are harder to keep the seals working well. At least everything mentioned is pretty cheap to do with no expensive or difficult substitutions in the program. I like cheap somewhat meaningful indicating tests myself. Perhaps not the necessity to do them though.

In fact, poor oil control can actually improve compression.