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
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
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
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
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
it has used .6 quarts which means in that interval you think it has gone
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?
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.
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
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
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.]
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.
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.
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.
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
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
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.
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.
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
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?
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
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.
"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
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
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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