All IC engines burn oil...

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So, I know from my engineering education and spending time here that every internal combustion engine uses a very small amount of oil with each power stroke.

The reason people are adament that their engine doesn't use oil is because the crankcase is also gradually filling up with unburnt fuel, or water that gives the dipstick a full reading even if the ratio of 100% engine oil in sump is not as it was at last change.

So my question is: For an engine with no external leaks, can there be a measure to determine what level of oil depletion is to be expected from the power cycle burn off x number of revolutions x number of cylinders?

Or is it all: let's build it and see what happens?
 
in my car the level does not change at all during its 5000km interval. It even gets redlined every once and a while. my uoa said 0% fuel. even when it's minus 45 out and gets short tripped it stays the same.
 
Oil use happens, I think the important point is wether or not the use is measurable on the dipstick.
I agree that other fluid can be introduced to the crankcase ad elevate the level but at the same time I feel that is more likely with short tripped engines, or any other that spends more runtime cold than hot.
There are plenty on here that see sustained high oil temps that burn that stuff off, some even use vacuum pumps to evacuate it - not to mention the dry sump guys..
So yeah, I think what you describe only applies in certain circumstances
 
I'm sure that the engineers who design and build engines know,

1) The ring-swept surface area of the cylinder that becomes exposed to combustion gasses each cycle (anyone can figure that out from the engine bore/stroke specs and the piston ring heights)

2) An estimate of the thickness of the oil film deliberately left by the ring pack on each downward stroke

3) An estimate of how much of that film is burned vs. how much is so tightly adhered to the cylinder wall that its "quenched" from burning by the cold wall.

Armed with all that, I'm sure you could calculate micrograms of oil per hour of operation.

I don't believe that the mechanism is that lost oil is replaced by combustion by-products, in certain operating regimes (high/extended load operation) the combustion byproducts just do not accumulate. I think so little oil is lost that its just not measurable over a normal OCI on such a crude measurement tool as a dipstick.
 
Originally Posted By: KGMtech
So, I know from my engineering education and spending time here that every internal combustion engine uses a very small amount of oil with each power stroke.

The reason people are adament that their engine doesn't use oil is because the crankcase is also gradually filling up with unburnt fuel, or water that gives the dipstick a full reading even if the ratio of 100% engine oil in sump is not as it was at last change.

So my question is: For an engine with no external leaks, can there be a measure to determine what level of oil depletion is to be expected from the power cycle burn off x number of revolutions x number of cylinders?

Or is it all: let's build it and see what happens?


That's what Subaru wants you to believe now...
 
I would be afraid that if you "lost" 1 qt of oil level due to oil "use",and it was replaced by a qt of fuel (which would mean it would appear no loss on the stick) that you would have serious wear issues not to mention severe flammability in the crankcase.
 
the oil level in my car hasn't deviated from full for the last 20,000 miles. I did add about half a quart in the first 7k, but the level never moved after that.
 
While it may be true that oil is burned by the engine, the amount however will vary from engine to engine from a few millilitres to litres.

In no way do I believe that is replaced by unburnt fuel or water. Just as consumption is not uniform across engines, how can 'replacement' be so equally precise year after year. My Corolla has no visible oil movement on the dipstick from beginning to end of the OCI. Its been that way since new. The LeSabre and Sierra has visible movement on the dipstick showing consumption depending on its workload and engine speeds.

I haven't had one, but UOA would show fuel...it is in % down to 0.5 increments from the reports I have seen.
 
Originally Posted By: friendly_jacek
Originally Posted By: abycat
my uoa said 0% fuel.


and what is the precision and accuracy of that test?


I am guessing good enough to notice a 1/4 quart or more of fuel making up the difference of the burned oil.
 
There are other substances that get dissolved or suspended in oil that can do this as well - soot, wear metals, etc.
 
Originally Posted By: friendly_jacek
Originally Posted By: abycat
my uoa said 0% fuel.


and what is the precision and accuracy of that test?


it was blackstone so I'm sure take it with a grain of salt but I'm pretty sure there is no fuel in it. level never changes one bit. I do check it every few trips out of the driveway it takes.
 
Originally Posted By: KGMtech
So, I know from my engineering education and spending time here that every internal combustion engine uses a very small amount of oil with each power stroke.

The reason people are adament that their engine doesn't use oil is because the crankcase is also gradually filling up with unburnt fuel, or water that gives the dipstick a full reading even if the ratio of 100% engine oil in sump is not as it was at last change.

So my question is: For an engine with no external leaks, can there be a measure to determine what level of oil depletion is to be expected from the power cycle burn off x number of revolutions x number of cylinders?

Or is it all: let's build it and see what happens?


Both water and fuel will evaporate away to just traces on a long highway cruise.

Microliter accuracy measurement is not rocket science. Getting ALL the oil to drain for precision measurement is the hard part.
 
Originally Posted By: 440Magnum
I'm sure that the engineers who design and build engines know,

1) The ring-swept surface area of the cylinder that becomes exposed to combustion gasses each cycle (anyone can figure that out from the engine bore/stroke specs and the piston ring heights)

2) An estimate of the thickness of the oil film deliberately left by the ring pack on each downward stroke

3) An estimate of how much of that film is burned vs. how much is so tightly adhered to the cylinder wall that its "quenched" from burning by the cold wall.


Here's a link to a paper that I posted in the technical and whitepapers about this time last year.

http://www.bobistheoilguy.com/forums/ubb...e_a#Post3372187

Quantifies the migration rate, residence time, and return rate into the ring pack.

Originally Posted By: Shannow
Behaviour, and degradation of lubricant in the ring belt.

Interesting paper looks at how long lubricants (and how much) hang around in the ring belt, and their movement back to the sump, or into the chamber.

Looks then at how the oil degrades, using a temperature controlled sump of 70C (and entirely separate valve train lube system) to ensure that the degradation/oxidation in the sump is controlled almost entirely from what's going on around the rings.

Really interesting measurements of residence time in the ring belt, versus how long the same oil stays in the sump...e.g. 0.41ml oil flow per minute per cylinder INTO the ring pack, 0.36ml oil flow per minute per cylinder out of the ring pack (0.05ml/min per cylinder goes missing - translate that in the 4 cyl version of the test engine, and 0.2ml/minute...946ml/qt, means 4,730 minutes per quart of consumption excluding dilution reducing the dipstick effect...or 4,730 miles at 60miles per hour for a quart consumed).

It stacks up with previous studies that I've read showing a concentration of additives in the ring belt, as the oil goes missing somewhat.

Rate of supply/drain back means that there's probably nearly never a truly "dry" start, and even 10 seconds of "starvation" after a start is unlikely to run the ring pack dry.

Interesting what sort of temperatures the ring belt runs at, and for how long the oil stays there...Noack in this region is significant, but doesn't mean 10% of your sump evaporates in an OCI.

BTW, engine is Vauxhaul based FWIW.
 
I don't think the consumed oil is completely replaced with gasoline. We see plenty of great UOA's with no oil added, no visible consumption and
The consumption is there, it just isn't visible on the dipstick.
 
I don't think that lost oil is being replaced with fuel and water.
Water doesn't last long in the crankcase of an engine regularly run at normal operating temperature and even fairly high fuel dilution wouldn't replace enough lost oil to maintain a constant oil level.
Rather, while all engines must consume some oil, the amounts of oil consumed by many are small enough to pass unnoticed.
This is why so many people post that their engines use no oil.
They must, but they don't use enough to notice on the dipstick.
We've had mostly "uses no oil" engines.
To me, this is no more than shorthand for consumption remaining low enough that it can be ignored for the length of a typical OCI.
It doesn't mean that the engine literally uses no oil.
 
Shannow, your access to the analyses on the most obscure, interesting, and arcane topics of lubrication continues to amaze me.

:)
 
The oil consumption in my 2 Toyotas is theoretical, and not measurable. My 4runner is so reliable in this trait that, after 248k miles, I just check the level after I fill it, and just before I drain it, to make sure. And there is no measurable fuel, water or coolant in their, either.

My Tacoma only has 100k of no measurable oil consumption, and I tow with it, so its level gets checked every other day when traveling. It turns its oil black, but no drop in level.

I am sure they both consume some. But it has to be less than an ounce per 1000 miles, so I will never see it on the dipstick.

My Subaru has used a small amount......Enough to notice on the dipstick......4-6 ounces in 5k miles. But, interestingly, only in the winter. Summer, crossing the mojave at 115 degrees, nada, zilch, nothing.
 
Originally Posted By: 440Magnum
Shannow, your access to the analyses on the most obscure, interesting, and arcane topics of lubrication continues to amaze me.

:)


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It's what I love about BITOG, gives me directions to keep learning.
 
The paper says .05 cubic centimeter per minute

.05 * 60 = 3cc per hour. At an average of 30mph a normal 5000mi oil change would have the engine running at 166.66 hours.

166.66 * 3 = 500 or half a liter

Tales of no oil consumption are tall ones, but I guess some guys get extremely turned on by the thought that their vehicle burns no oil. That's the only explanation I can come up with.
 
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