Tegger's real-world oil consumption

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Thanks.
But "jim" actually did have a couple of good points buried within his invective. I've adjusted the PDF to address those points. And I'm going to see if I can determine exactly what is the degree of linearity of the dipstick readings.
--
Tegger

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That's a good point, and one I hadn't explicitly considered.
I have noticed, though, that if the stick shows, say, 0.8 low on my paper chart and I add 0.8, the level goes back up to its position during the first check for that 1,00 miles. The same thing happens if the level is down 0.4 on the chart. I therefore had no reason to suspect that the level might not decline linearly.
But since it's a possible variable that I need to account for (now being aware of its possible existence), this is something I'm going to have to confirm.
--
Tegger

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Tegger wrote:

    The point I have been making is your PDF file is itself strong evidence that your measurements and calculations are flawed. I can tell you there is very little doubt that the error exists. I would estimate there is a one in a million chance that the measurements and subsequent calculations shown in the PDF are at all close to correct. I believe the oil is being consumed at a fairly steady rate. The wild fluctuations are nothing but evidence that the measurements and calculations are inaccurate. The fact that the fluctuations are not at all random suggests that the error is due to a measurement bias. The bias makes it appear that typically more oil is being consumed in the first 1000 than in the second 1000. But in reality the general difference that is found the first and second readings is probably due to something other than the actual consumption.     Whether you are interested in finding the source of the error is your call. no one else is in a position to investigate. On the other hand you can circle the wagons and try to defend the foolishness. It's your call.
    One thing to consider is oil at 2500 miles looks different than fresh oil. And your measurements and calculation entirely depend on how the oil looks on the dipstick, so that is one possible source of a measurement bias.
    The suspicion that the error comes from the irregular shape of the pan was based on the assumptions made at that time (which I posted). There could be a small region on the dipstick where there is a non linearity. If your first 1000 mile measurement tends to be below that spot and the second above then you could be getting large difference where in reality both measurements are close to the same.
    I will state my current assumptions based on some new info in case you're interested:
1) At 3000 miles you change the oil. When you fill with fresh oil the level on the dipstick is a bit below full.
2) After somewhere in the neighborhood of 1000 miles you infer that it has used about .7 quarts which would make you think it went around 1400 miles/qt. In reality the engine has really only used .6 quarts at that point in the cycle which means it has really gone 1670 mi./qt. At this point you add .7 quarts of oil and that bring it up to tad over full (.1 higher than it started).
3) At around 2000 miles you check the oil and infer from your measurements that it has used .6 quarts which means in that interval you think it has gone 1670 miles/qt. But in reality it has used a .61 quarts on this part of the cycle (pretty much the same as the first 1000 miles). That means it has actually used 1640 mi/qt. in this interval. You then add .6 quarts and that brings it back to full mark.
4) At 3000 miles your chart indicates you don't do any measuring/recording data you just change the oil and repeat the process which again repeats roughly the same errors.
    Notice that I used 1000 mile intervals but your PDF file makes it clear the 1000 mile intervals is most of the time just a fiction.     Also, there should have been 43 dipstick reading in 42000 miles, but only 25 of these were recorded. Did you not like what you saw on the dipstick on those other occasions? n other words. what bias was introduced by selecting only 40% of the possible samples. What about the 13-14 time the that engine reached the 3000 mile mark? Are we to believe you never once looked at the dipstick to determine and record how much was used in the 2000-3000 mile sampling interval?
-jim     

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Definitely. 2,500-mile-old oil is darker and easier to see on the stick. I do find it a bit difficult to locate the top of the "meniscus" with brand- new oil, since it's so clear. It is possible that my second check is more accurate than my first, for this reason.

A fresh batch of Mobil 1 went in this evening. I took the opportunity to try and determine exactly where the "live" area of the dipstick was in relation to the oil pan.
The bottom of the dipstick is, as far as I can measure, about an inch below the bottom surface of the oil pan mounting flange. A bit below that point is when the pan's "shallow" area suddenly takes a dip into the "deep" area.
The "shallow" area slopes downwards maybe 1/4" from the flywheel end to the "deep" end, maybe a 6" distance. It then takes about a 12mm radius and then heads straight down to the drain bolt.
Based on these observations, I believe the oil level does drop fairly linearly, since there is no drastic change in oil pan shape from upper mark on the stick to lower mark on the stick.
--
Tegger

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Tegger wrote:

I don't know why you're changing oil every 3K. Any reputable oil such as Castrol, Valvoline etc should be good for at least 5K.
JT
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On 05/30/2010 05:52 PM, Grumpy AuContraire wrote:

indeed. he's using mobil 1 - he should be looking at 10k at least.
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On 05/28/2010 05:13 PM, Tegger wrote:

dude, with the greatest of respect, and don't take my pedantry personally, but there are a number of things here which are really bad practice and a correspondingly bad example for other users.
1. you're dipping the oil too long after shutdown. you should be following the procedure honda specify - "a couple of minutes after shutting the engine off". it is the only consistent method available to all users, all conditions. you are an adherent of the owners manual after all...
2. your change intervals for the oil you're using is way too short. i can see a shorter interval if you're trying to de-gum an engine that's been abused, but here, you're wasting both money and resources. if you want to spend the money on something useful, spend it on analysis, not wasting oil.
3. don't over-think this meniscus thing. all you need to do is ensure consistency. if you're serious about making quantitative measurements [as opposed to monitoring trends - the real objective here], install a sight tube and vernier. and make sure you take thermal expansion into account. see #2.
4. again re #2., you should allow for batch differences in the base oils. mobil /do/ use a proportion of group III in their base, and that proportion varies from batch to batch. it stands to reason that the gIII's greater propensity to breakdown will give you variance in consumption levels in line with content proportions. what you should do is stick to a longer interval and you'll find that the aggregate total over the full cycle is more consistent. the rate of consumption drops as the volatiles burn off, so this will have a better averaging effect that is more consistent with your vehicle's consumption over the use cycle, not reflecting the oil's composition and initial burn-off rates. [you can also try mobil's eco or extended performance blends - a lower proportion of gIII's and in my experience, lower oil consumption.]
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On 06/01/2010 06:13 PM, jim beam wrote:

oops, forgot to mention:
among other reasons, oil temperature and whether or not the oil filter's anti-drain-back valve is functioning are factors here. dipping at full working temperature is consistent. dipping before drain-back happens is consistent. anything else is subject to considerable variance.

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On 6/1/2010 9:21 PM jim beam spake these words of knowledge:

Checking your oil every day before the engine is started is consistent, and tells you how much oil you have in your system. As Tegger pointed out, you want to do it while the car is in the same physical location as well, to eliminate vagaries of level.
RFT!!! Dave Kelsen
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On 06/02/2010 04:14 AM, Dave Kelsen wrote:

consistently wrong. for the reasons stated above, it needs to be checked after the engine has attained full working temperature and has been shut down for "a couple of minutes". like when you've pumped gas. all gas forecourts are level. just dip the oil when you fill up. like it says in the honda manual.

no, dipping when cold doesn't. it doesn't allow for temperature differences, and it doesn't allow for filter drain - i.e. whether or not the anti drain-back valve is functioning. filters are very inconsistent in that - tegger should know - he's written about it before.
again, the only consistent and accurate method is to dip as above. after all, it's where the dip stick marks are positioned to be read - there is always a difference between hot and cold, and honda are positioned to be read hot.

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Measuring engine oil consumption in this manner is difficult. While you definitely can measure the volume of fluid in the crankcase, that way not mean much unless you also know the make-up of the fluid in the crankcase.
All piston engines consume some oil. They must. A thin layer of oil remains on the cylinder wall on every piston stroke. Some of this is burned during the combsution process, some vaporizes and leaves with the exhaust, etc. Even in a very well sealed engine, more oil leaves via the valve stems, the crank seals, through the PCV system, etc. More of the original oil leaves as light components of the oil boil away.
Balancing the oil that is consumed is comtamination added to the crankcase via blow-by past the rings, through the PCV system, air exchanged with the atmosphere, and in some cases minor leakage from the cooling system. This contamination takes several forms - water, unburned hydrocarbons, soot, dust particles, etc. Some of this contamination ends up in the oil filter, but much of it remains suspended in the "oil" in the crankcase. Some of these contaminates have realtively low boiling points and can be driven off if you get the "oil" hot enough. Others don't boil off. The fact that the oil changes color is evidence that some contamination remians.
When you first change your oil, you have a crankcase full of pure oil. A thousand miles later, the crankcase is now filled with a mixture of oil, water, soot, unburned hydrocarbons, dust and ? If you check the oil level immeadiately after a long drive which has rasied the temperature of the oil above the boiling point of water, you can assume that most of the water, and much of the unburned hydrocarbons have been vaporized and are not immeadiately contributing to the oil level in the crankcase. But soot, some unburned hydrocarbons, and dust are still present. It seems reasonable to assume these are of only minor significance, and that the decrease in oil level really does represent oil consumed. However, if you check the oil after several days of short trips in cooler weather, it is likely there is still significant volumes of water and unburned hydrocarbons in the crankcase contributing to the oil level. I am not sure how you can manage the measuement process to consistently guarantee that you have driven off the water and unburned hydrocarbons to the same extent?
You might think this is a trivial problem. I don't. On my farm we had a very old gas tractor. The combustion rings did not seal well and the tractor suffered from massive blow-by. We typically just used the tractor to pull a trailer, or move a scoop load of grain for the cows (it had a front end loader). Much of the time the oil level in the crankcase stayed level or actually increased. Occasionally we would work the tractor harder (for instance using the loader to move a pile of dirt). In these cases, the oil level would drop dramitically. I never bothered to have the oil analysed but I suspect that after just a few months of light usage it included a very high percentages of water and unburned hydrocarbons.
Another factor would be when and under what conditions you add make-up oil. The rate of oil consumption should increase as the composition of the oil in the crankcase changes. I believe that the "fresh" oil probably has a realtively low given burn off rate. As the composition of the oil changes, this burn off rate changes as well. What is left of the original oil is likely more viscous and likely burns off at a lower rate. However, the contamination that has accumulated in the oil probably has a much higher burn off rate. So for a engine with weak / worn rings and seals, the percentage of "original" oil steadily decreases but at decreasing rate. I am guessing that you might see a realtively quick decrease initially, followed by a long slow increase in usage that levels out, asusming you add fresh oil regularly to compensate for usage. At some point you are replacing contaminated original oil with fresh oil in such a way that you reach a sort of steady state composition (and burn off rate) for the oil.
Ed

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"Light components" of the oil do NOT "boil away". That is, flat-out, a myth. I have this on /very/ good authority.
As for oil burn-off, well yes, that is precisely what I am trying to measure.

Water is not an issue here, trust me. Fuel, however, is. The one analysis I had done in 2005 indicated that I had about 2% dilution after 3,000 miles.

Soot and dust make up the smallest part of the oil, by far. There isn't nearly enough there to affect the level.
--
Tegger

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On 06/07/2010 06:53 PM, Tegger wrote:

sorry dude, your "authority" has that very wrong - they clearly have never done fractional distillation.

that contradicts statement above...

that's not good, especially not for a vehicle making longer runs like yours. did you rectify the problem?

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My sources do fractional distillation for a living.
The "boil-off" thing is, flat-out, totally, completely, utterly, absolutely, wholly wrong in every possible and imaginable way.

"Burn-off" means consumption via worn rings and seals, not evaporation due to some sort of "boil-off".

I don't know; I never did another analysis.
Considering that there apppears to have been very little change in oil consumption since 2005, and considering the oil-light still goes off about as quickly as the one in our 130K mile Toyota Tercel, I think the amount of fuel in the oil is not creating a panic situation.
--
Tegger

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On 06/08/2010 05:24 PM, Tegger wrote:

no it's not - it's the fundamental principle of distillation. motor oil is a mix. that means means there are different components. different components have different boiling points. and that's /before/ there's any breakdown, which by definition means different boiling points all over again.
either we need to re-write the chemistry books, or you're somehow asking your sources a question that's got them talking about a different point than than the one we're discussing.

it doesn't burn until it vaporizes. it doesn't vaporize until it gets heated. and when it get s heated, some fractions vaporize [evaporate] before others. see above.

are you not interested in the fact that you're apparently wasting gas?
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On 06/08/2010 05:54 PM, jim beam wrote:

further reading: http://www.chemguide.co.uk/physical/phaseeqia/idealfract.html

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Have you considered that the evaporable fractions may have been removed when the oil was made?
Have you considered that oil is /not supposed/ to evaporate, and may have been /designed/ not to evaporate?

I think the wastage is very, very tiny.
My crankcase contains, nominally, 135 ounces. 2% fuel inside that 135 ounces works out to about three ounces. And that's after 3,000 miles.
Any fuel not absorbed by the oil is finding its way back into the intake via the PCV system. Which, of course, is exactly why the PCV system was devised in the first place...
I can also tell you that any fuel in my oil is undetectable by my nose, even when I compare/sniff brand-new oil and the stuff I just drained. I once had a fuel-pump diaphragm break with my '75 Corolla. Oh BOY did that oil ever smell of gasoline!!
BTW, my oil analysis was done in 2006, not 2005. I misread the report before. I might get another one done, just to see if high-fuel still presents itself.
--
Tegger

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On 06/08/2010 06:17 PM, Tegger wrote:

yes indeed. but that link i carefully gave you, and which you have equally carefully snipped, discusses evaporation with respect to solutions. you should read it.
as for the question you've asked your sources, i suspect it was along the lines of whether oil boils at operational temperatures and the answer of course is "no". but if you read and think about the link i gave you, and employ some common sense [how does motor oil have a smell if it's not losing vapor from its surface?], then you'll see some logic in what i'm trying to communicate.

well, according to the argument you've been using above, that would be impossible. this is why it's important to understand the principles.

that would be good.
the reason i raise it is because that's a high percentage for a vehicle that runs for extended periods at full working temperature and thus should be seeing it all evaporate. to be retaining that percentage, it has to be being "replenished" at quite a rate, and that is costing you money. if it was just a townie runabout, colder average operating temps and shorter durations would mean lower evaporation and that percentage might be less of an issue.
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"Carefully" snipped? More like the opposite. I like to keep my posts at less than book-length, so I snip regularly
Anyway, I actually did read that link. In that page, I found the following: "So what about the liquid left behind at each reboiling? Obviously, if the vapour is richer in the more volatile component, the liquid left behind must be getting richer in the other one.
"As the condensed liquid trickles down the column constantly being reboiled by up-coming vapour, each reboiling makes it richer and richer in the less volatile component - in this case, A. By the time the liquid drips back into the flask, it will be very rich in A indeed."
Which is /exactly/ what I was saying. You remove the lighter fractions so that what is left is what /does not/ boil off under the sort of temperatures experienced by motor oils.

Cheese smells too. But it does not evaporate. Tires smell. Do they evaporate? Do either of those change volume detectably in the course of smelling?
--
Tegger

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On 06/09/2010 02:30 PM, Tegger wrote:

but you shouldn't be snipping the relevant bits. and you did in this case.

no you weren't. you were saying that oil does not lose anything through vaporization. i was telling you that it does, and that although the oil may not boil - something you were fixated on - it /will/ lose its lighter fractions.

but dude, you're contradicting yourself - the lighter fractions do indeed vaporize, and you are left with the heavier fractions. that is why you've been recording oil losses. that is why there are vaporization loss tests. this /starts/ when you fill the engine with new oil, and you have losses from that point on. if you left your oil in for a longer [more reasonable] period, you'd also notice the rate of consumption drop once the volatiles have disappeared - again, exactly as those phase diagrams tell you it would.

ok, go ahead and weigh some fresh cheese on a gram-accurate scale, leave it out for a day, then re-weigh it. report back.

they are losing their lighter volatile components, absolutely.

volume is not mass. and absolutely, the mass loss is easily detectable. do your cheese experiment and report back.
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