Never change oil, only filter?
- Thread starter JoeWeinstein
- Start date
- Status
Originally Posted By: scoobie
no, it doesn't work that way, because the oil u put in 4000 miles ago is still mainly there, and worn out. keep doing what you suggest and you're in for an engine rebuild, i would say, in about 30,000 miles, if you're lucky.
How do you say so? If the motor burns 1 qt per 1000 miles,
is there some mechanism that makes it burn the most recently
added oil as opposed to the older oil? I don't think so. I
think the constant oil circulation gets it essentially blended
on a continual basis so you're burning, and running oil that
has the aggregate properties of oil that has been used for
2500 miles.
no, it doesn't work that way, because the oil u put in 4000 miles ago is still mainly there, and worn out. keep doing what you suggest and you're in for an engine rebuild, i would say, in about 30,000 miles, if you're lucky.
How do you say so? If the motor burns 1 qt per 1000 miles,
is there some mechanism that makes it burn the most recently
added oil as opposed to the older oil? I don't think so. I
think the constant oil circulation gets it essentially blended
on a continual basis so you're burning, and running oil that
has the aggregate properties of oil that has been used for
2500 miles.
Yes, UOA would be prudent when filters were changed.
OVERKILL
$100 Site Donor 2021
Originally Posted By: scoobie
no, it doesn't work that way, because the oil u put in 4000 miles ago is still mainly there, and worn out. keep doing what you suggest and you're in for an engine rebuild, i would say, in about 30,000 miles, if you're lucky.
Are you seriously disagreeing with Doug?
no, it doesn't work that way, because the oil u put in 4000 miles ago is still mainly there, and worn out. keep doing what you suggest and you're in for an engine rebuild, i would say, in about 30,000 miles, if you're lucky.
Are you seriously disagreeing with Doug?
Originally Posted By: OVERK1LL
Originally Posted By: scoobie
no, it doesn't work that way, because the oil u put in 4000 miles ago is still mainly there, and worn out. keep doing what you suggest and you're in for an engine rebuild, i would say, in about 30,000 miles, if you're lucky.
Are you seriously disagreeing with Doug?
Just disagreeing with the particular argument.
Originally Posted By: scoobie
no, it doesn't work that way, because the oil u put in 4000 miles ago is still mainly there, and worn out. keep doing what you suggest and you're in for an engine rebuild, i would say, in about 30,000 miles, if you're lucky.
Are you seriously disagreeing with Doug?
Just disagreeing with the particular argument.
OVERKILL
$100 Site Donor 2021
Originally Posted By: JoeWeinstein
Originally Posted By: OVERK1LL
Originally Posted By: scoobie
no, it doesn't work that way, because the oil u put in 4000 miles ago is still mainly there, and worn out. keep doing what you suggest and you're in for an engine rebuild, i would say, in about 30,000 miles, if you're lucky.
Are you seriously disagreeing with Doug?
Just disagreeing with the particular argument.
I meant scoobie, not you bud. Your post was building on what Doug had said....
-Chris
Originally Posted By: OVERK1LL
Originally Posted By: scoobie
no, it doesn't work that way, because the oil u put in 4000 miles ago is still mainly there, and worn out. keep doing what you suggest and you're in for an engine rebuild, i would say, in about 30,000 miles, if you're lucky.
Are you seriously disagreeing with Doug?
Just disagreeing with the particular argument.
I meant scoobie, not you bud. Your post was building on what Doug had said....
-Chris
Last edited by a moderator:
Originally Posted By: JoeWeinstein
Yes, let's assume that the oil lost is not leaked externally,
but burnt, due to some combination of ring, valve, and other
wear. Let us also assume that the oil consumption doesn't
cause any other problem, and the wear or tolerances that
allow the oil loss are not getting any worse.
For those that don't understand it, if such a car consumed
zero oil, and you changed the 5 qts every 5000 miles, you
would similarly be running with oil at an average age of
2500 miles, but for some time you would be running with
a whole crankcase of 4500-mile-old oil, whereas with the
car described originally in this post, the car never runs
with oil (as a whole) older than 2500 miles.
And to make it simpler, for a car that doesn't leak *or*
burn any noticeable amount of oil, it would be like draining
1/2 qt every 500 miles, and topping off with fresh. No
need to ever drain the sump, right?
For somebody registering and asking a question on an oil forum, you've already put quite a bit of thought into this...
But in case you're serious, I'd change the oil out twice a year just to drain out any contaminants. And if you're worried about user a thicker oil, well, the oil you've used hasn't protected enough to prevent engine damage/deposits. Has it?
Yes, let's assume that the oil lost is not leaked externally,
but burnt, due to some combination of ring, valve, and other
wear. Let us also assume that the oil consumption doesn't
cause any other problem, and the wear or tolerances that
allow the oil loss are not getting any worse.
For those that don't understand it, if such a car consumed
zero oil, and you changed the 5 qts every 5000 miles, you
would similarly be running with oil at an average age of
2500 miles, but for some time you would be running with
a whole crankcase of 4500-mile-old oil, whereas with the
car described originally in this post, the car never runs
with oil (as a whole) older than 2500 miles.
And to make it simpler, for a car that doesn't leak *or*
burn any noticeable amount of oil, it would be like draining
1/2 qt every 500 miles, and topping off with fresh. No
need to ever drain the sump, right?
For somebody registering and asking a question on an oil forum, you've already put quite a bit of thought into this...
But in case you're serious, I'd change the oil out twice a year just to drain out any contaminants. And if you're worried about user a thicker oil, well, the oil you've used hasn't protected enough to prevent engine damage/deposits. Has it?
A classic calculus problem here folks. Let's assume a 5 qt system that loses 1 qt per 1000 miles as per the OP. Let's also assume an initial fresh oil change with five new quarts. 1000 miles down the road we lose a quart and we add one new quart to bring the system up to 5. At this point the average mileage on the oil is 800 miles. We travel 1000 more miles losing another quart. However, due to the continuous mixing of the old and new (at the 1000 mile mark) we lose 1/5 of a quart of the oil with 1000 miles on it and (1/5) of the 4 quarts with 2000 miles on it. We add one more quart to bring of fresh oil to bring us back to five quarts. At this point (2000 mile mark) we have 1 quart of fresh oil, (4/5) of a quart of oil with 1000 miles on it and 4*(4/5) quarts with 2000 miles on it. At this point the average mileage on the oil is 1440 miles with 3.2 quarts of the original oil. This continues (yielding a geometric series if anyone cares) . . .
At 5000 miles we have an average oil life mileage of 2689 with 1.6 quarts of the original oil.
At 10,000 miles we have an average oil life mileage of 3570 with 0.5 quarts of the original oil.
At 15,000 miles we have an average oil life mileage of 3859 with 0.17 quarts of the original oil still around!
In the long run, the average oil life mileage tends to 4000 (*not* 2500) with a trace of the original oil still around.
At 5000 miles we have an average oil life mileage of 2689 with 1.6 quarts of the original oil.
At 10,000 miles we have an average oil life mileage of 3570 with 0.5 quarts of the original oil.
At 15,000 miles we have an average oil life mileage of 3859 with 0.17 quarts of the original oil still around!
In the long run, the average oil life mileage tends to 4000 (*not* 2500) with a trace of the original oil still around.
Last edited:
The above seems accurate, and if dino near the lifetime limit of this. A 15 k oil would have been changed 3 or so times, so this stuff at 4k miles will have 3-4 times the sludge producing precusors, and given them plenty of time to stick together and to everything else. AS I say seem accurate, but if I knew say the TBN at 15k I would feel better using or not.
Cool! thanks for the math! So if the oil is one of those
7.5k or 15k extended service oils, we're, well, OK. (And
I appreciate that we agree that the oil is continuously
mixed).
I assume all contaminants are and sludge precursors burnt
along with the oil, in the percentages they exist. I don't
see any mechanism for their preferential retention, any more
that the old oil would be preferentially retained....
Joe
7.5k or 15k extended service oils, we're, well, OK. (And
I appreciate that we agree that the oil is continuously
mixed).
I assume all contaminants are and sludge precursors burnt
along with the oil, in the percentages they exist. I don't
see any mechanism for their preferential retention, any more
that the old oil would be preferentially retained....
Joe
Last edited:
I'm in the same situation you are only worse...my '94 Crown Vic Police Interceptor with unknown miles (broken odometer) is going thru a qt every *estimated* 300 to 500 miles...I've heard that this year model had "bad" valve seals and that is probably where the oil is getting thru..its been run like this for two years and it runs very well with no issues such as spark plug fouling..and yes, I've changed the PCV valve. It sees limited use so the annual mileage is low and I just change the oil filter for it's last annual "service"....I thought about using Auto RX but if it's a known bad seal condition, I didn't know if the ARX could help it or if it would be in circulation long enough to help it...does anyone know what was the exact problem with the seals on these engines???
Sorry for the semi Hi Jacking....btw, what is your vehicle..
Sorry for the semi Hi Jacking....btw, what is your vehicle..
I guess my main point is that one doesn't get to direct the oldest most worn out oil to be what is lost on any 1000 mile run . . . we lose of fraction of the oil 1000 miles old, a fraction of the oil 2000 miles old, a fraction of the oil 3000 miles old and so one with each 1000 miles traveled.
The original fill oil will always be present (although in ever decreasing amounts). The oil added at the 1000 mile mark will also always be present for all future time and so on. The continuous mixing of 1 new quart and all the varied old oils means over time the oil has an average *mileage* of 4000.
With respect to your question on contaminants, if the rate at which contaminants accumulate in the oil is proportional to the miles driven (an extreme simplifying assumption!!), then another geometric series shows that the contaminant level in the long run would be comparable to that in the oil at the *end* of a 5000 mile OCI. Under these simplifying assumptions, one is running 4000 to 5000 mile oil in their vehicle all the time if one does nothing more than replace the lost 1 quart every 1000 miles.
Of course, changing the filter periodically improves the above numbers. Also, simplifying assumptions are probably best left in a calculus one (or physics) class and not applied too seriously to the real world.
The original fill oil will always be present (although in ever decreasing amounts). The oil added at the 1000 mile mark will also always be present for all future time and so on. The continuous mixing of 1 new quart and all the varied old oils means over time the oil has an average *mileage* of 4000.
With respect to your question on contaminants, if the rate at which contaminants accumulate in the oil is proportional to the miles driven (an extreme simplifying assumption!!), then another geometric series shows that the contaminant level in the long run would be comparable to that in the oil at the *end* of a 5000 mile OCI. Under these simplifying assumptions, one is running 4000 to 5000 mile oil in their vehicle all the time if one does nothing more than replace the lost 1 quart every 1000 miles.
Of course, changing the filter periodically improves the above numbers. Also, simplifying assumptions are probably best left in a calculus one (or physics) class and not applied too seriously to the real world.
Since you are not burning all old oil, the particle count should be going up.Eventully it will get to the carry limit of oil. This is like your gas tank I think, you add gas with contaminants, and pump most out, then refill new gas and a new load of particles. This gas at bottom of tank is the worst stuff, and is why not recomended to run tank dry for fear of ingesting this stuff into fuel system. Sludge precursors are somewhat soluable in oil, and some less so. Time seems to be a factor with them altering and sizing up enough to accumulate on engine parts. Some are not as burnable, and at higher loads can make it via oil into ring pack and stick it up, especially if a lot of extra oil in cylinder.
Originally Posted By: JoeWeinstein
Originally Posted By: BuickGN
Originally Posted By: JoeWeinstein
No, let's say I'm running the correct viscosity for my
motor... No one should run thicker, just to stop
consumption. That's like turning your blood to jelly,
to stop a hangnail from bleeding.
I'm surprised my TL is still running with that Jelly going through it's veins.
I am only saying that you should run the viscosity
recommended for your engine, and not put in any
thicker oil, just to stanch a symptom. If 20w50 is
right for your car, that is what you should run,
but if it was supposed to use 10w40, and now it's
older, somewhat tired etc, I don't think you want
to thicken your oil. It may stop consumption, or make
the valve train quieter etc, but I worry that it
will still cause extra wear, at startup when thin
oil is good, and also may not adequately lubricate
those parts of your motor that still have the original
gaps that require the thinner oil. For instance, in
trade for less oil past your worn rings, you may also
be getting less oil through your still-OK main bearings...
I wouldn't sacrifice or jeopardize my bottom-end for
any savings of a qt. per 1000 miles. I'd either get
my top-end rebuilt or live with it.
You don't want pressure, you want flow. Viscosity
is liquid friction, a necessary evil to be accepted
only as much as necessary. Formula 1 engines use very
thin oils, like straight 0-wt. Do what the manufacturer
says....
So, back to the original question; and it's sounding
like if the oil qualities are such that it's perfectly
adequate at 2500 miles of use (assuming the motor's
blow-by etc does not unusually dilute or use up the
oil's additives enough to defeat the oil's normal
recommended life) it sounds like the idea is not wrong.
Joe
Going up one range in viscosity won't hurt a thing. I run a higher than recommended viscosity in all of my cars, always have and not once have I had a problem.
If you had ever watched how quickly an engine gets oil pressure, even with thicker stuff in the winter, you wouldn't be worried. With a 20-50 in my GN, oil is coming out of the valvetrain nearly instantly. Oil is coming out of the turbo feed before I release the ignition key.
As long as if flows ok, you're fine. I believe the thin stuff is primarily for fuel economy while warming up.
Originally Posted By: BuickGN
Originally Posted By: JoeWeinstein
No, let's say I'm running the correct viscosity for my
motor... No one should run thicker, just to stop
consumption. That's like turning your blood to jelly,
to stop a hangnail from bleeding.
I'm surprised my TL is still running with that Jelly going through it's veins.
I am only saying that you should run the viscosity
recommended for your engine, and not put in any
thicker oil, just to stanch a symptom. If 20w50 is
right for your car, that is what you should run,
but if it was supposed to use 10w40, and now it's
older, somewhat tired etc, I don't think you want
to thicken your oil. It may stop consumption, or make
the valve train quieter etc, but I worry that it
will still cause extra wear, at startup when thin
oil is good, and also may not adequately lubricate
those parts of your motor that still have the original
gaps that require the thinner oil. For instance, in
trade for less oil past your worn rings, you may also
be getting less oil through your still-OK main bearings...
I wouldn't sacrifice or jeopardize my bottom-end for
any savings of a qt. per 1000 miles. I'd either get
my top-end rebuilt or live with it.
You don't want pressure, you want flow. Viscosity
is liquid friction, a necessary evil to be accepted
only as much as necessary. Formula 1 engines use very
thin oils, like straight 0-wt. Do what the manufacturer
says....
So, back to the original question; and it's sounding
like if the oil qualities are such that it's perfectly
adequate at 2500 miles of use (assuming the motor's
blow-by etc does not unusually dilute or use up the
oil's additives enough to defeat the oil's normal
recommended life) it sounds like the idea is not wrong.
Joe
Going up one range in viscosity won't hurt a thing. I run a higher than recommended viscosity in all of my cars, always have and not once have I had a problem.
If you had ever watched how quickly an engine gets oil pressure, even with thicker stuff in the winter, you wouldn't be worried. With a 20-50 in my GN, oil is coming out of the valvetrain nearly instantly. Oil is coming out of the turbo feed before I release the ignition key.
As long as if flows ok, you're fine. I believe the thin stuff is primarily for fuel economy while warming up.
Thanks for the chat guys!
This was a hypothetical, but an interesting one to me,
and it was good to be schooled that it'd devolve to
constant 4000-mile oil.
This was a hypothetical, but an interesting one to me,
and it was good to be schooled that it'd devolve to
constant 4000-mile oil.
There is a troll operating in this thread.
Cornfused: Yep - I joined in 06 and I've lurked here for a long time. This is the first time I felt I had something constructive to add to a discussion thread.
In the distant past I supported myself as a truck / heavy equipment mechanic . . . but I ended up getting a PhD in pure mathematics (a real disappointment to my father who actually built things as an electrical engineer!) and I teach at a regional university these days (still swinging a wrench to maintain two off-road motorcycles my son and I race).
In the distant past I supported myself as a truck / heavy equipment mechanic . . . but I ended up getting a PhD in pure mathematics (a real disappointment to my father who actually built things as an electrical engineer!) and I teach at a regional university these days (still swinging a wrench to maintain two off-road motorcycles my son and I race).
I'm not suggesting that you do it, but I have done what you are asking with my old Dodge Caravan which as burning through the same amount of oil. I did this for 100,000KM (60,000 Miles) and it never got any worse or better... FWIW.
Honestly, I don't think that you will have a problem. As long as the oil is holding the contaminants in suspension (and it should with an avaerage age of 4,000 miles), they are going past the rings and guides (or out the leak) with it.
As suggested an annual filter change adds another slug of fresh oil/adds, dropping the average even further.
The spacebears oil life study showed that even a couple of ounces every 1,000 miles did reach an "equilibrium" in terms of Fe content, and oil condition.
My Nissan is 73,000km old, and has had 9 oil changes. Statistically, there's some 73,000km OEM 10W-30, 70,000DeloCXJ...etc.
As suggested an annual filter change adds another slug of fresh oil/adds, dropping the average even further.
The spacebears oil life study showed that even a couple of ounces every 1,000 miles did reach an "equilibrium" in terms of Fe content, and oil condition.
My Nissan is 73,000km old, and has had 9 oil changes. Statistically, there's some 73,000km OEM 10W-30, 70,000DeloCXJ...etc.
- Status
Similar threads
