Oil consumption / oil level: linear or non-linear

[KitaCam]

I've been wondering...and does anyone know.....

Does oil consumption/burn-off increase more per mile as oil level decreases from "F" to "0" and below...?

That is....will more oil burn off per mile as oil level decreases, especially at extremely low levels?

 

[Phishin]

A lot of people think oil consumption increases as the crankcase has more oil in it. I guess their thinking is that more oil is being splashed up/slung onto the bottom of the pistons.....causing more oil to get by rings and causing oil to be consumed.

I guess thats their theory.....

 

[RiceCake]

More likely as oil level decreases, your oil will be more abused (sheared) and its more likely you'll start losing it faster.

But at the same time I lose oil rapidly at the start of an OCI, about a half a quart, and then it never burns a single drop.

So, you're asking for science in a system that is hugely chaotic. Im sure some cars are linear, some aren't.

 

[KitaCam]

Originally Posted By: RiceCake
More likely as oil level decreases, your oil will be more abused (sheared) and its more likely you'll start losing it faster.

But at the same time I lose oil rapidly at the start of an OCI, about a half a quart, and then it never burns a single drop.

So, you're asking for science in a system that is hugely chaotic. Im sure some cars are linear, some aren't.


....and yet another possible oil use/consumption progression I hadn't considered.

Thanks....

 

[RiceCake]

I blame my initial consumption on either air bubbles in the filter/system settling out, causing the oil level reported to drop, or some of the light oils burning off at the start of my OCI.

 

[Kuato]

Might be vehicle dependent. On our Wrangler, it will accelerate as the oil ages;but up to about the 1/2 way point through the OCI, doesn't burn any. Different brands also burn at different rates.

 

[Ibrahim]

Many reasons, usually oil loss/consumption will increase as the car ages and it also depend on the style of driving. Although, a very well maintained/clean engine would ward off oil loss pretty well...

I usually do not notice any difference in oil loss rate in my Odyssey regardless of what brand Synthetic 20 grade oil I use. So far, the consumption seems to go up slightly in winter time and in summer oil loss is barely measurable.

I think oil loss most likely is non-linear, and the rate of loss should increase as well as the oil loss increases.

 

[Colt45ws]

I dont lose any at the beginning to about 75% of the OCI then it starts going down. Still only lose about .25-.5 qt. There probably is some prior to that point but I dont notice it.
Over filling will eventually cause more burning and I suspect that at some point and under fill will cause increased consumption as well.

 

[kr_bitog]

Originally Posted By: KitaCam
I've been wondering...and does anyone know.....

Does oil consumption/burn-off increase more per mile as oil level decreases from "F" to "0" and below...?

That is....will more oil burn off per mile as oil level decreases, especially at extremely low levels?

It depends, when the oil have fuel dilution or the crankcase shape like V where the bottom area is smaller, it is possible for the oil seems burns faster

For other, the oil may burn faster when it is new when the oil viscosity is low, and stop burning after the oil thicken

It is just too many variables that cause it

 

[KitaCam]

Originally Posted By: kr_bitog


It is just too many variables that cause it


Good points all...but...

For my curiosity, can we assume ALL variables remain constant?
e.g. for any ONE vehicle, driving conditions remain the same...etc.

 

[Virtuoso]

On our cars that had any measurable oil consumption, it was always pretty linear. Even at a quart low, they were still burning off at about the same rate as before. If it was different, it was undetectable using dipsticks and eyeballs.

That's from a Saturn that did a quart every 300-400 miles, and a Malibu that did a quart every 2,000, a Mustang that did about the same, etc. It's not scientific, but all the cars generally were driven the same way, most of the time.

 

[javacontour]

Depends on the reason for consumption.

If it's a mechanical issue, I would expect it to be largely linear.

If it's an issue with the oil, as the additives break down in the oil, the rate of consumption rises.

As you lose oil, the remaining oil is stressed much more, causing a more rapid consumption.

The above is assuming other variables are the same, such as how the vehicle is driven.

 

[KitaCam]

yes Java...and my thought is, as oil level gets low, the engine is stressed even more, right (?) causing even more oil consumption...maybe.

 

[javacontour]

One of the jobs of oil is to carry heat away from parts that are not water cooled. The lower the oil level in the sump, the same heat must be carried away by less oil.

I imagine it's easier to "vaporize" more oil in this circumstance, causing the problem to feed on itself.

Originally Posted By: KitaCam
yes Java...and my thought is, as oil level gets low, the engine is stressed even more, right (?) causing even more oil consumption...maybe.

 

[rationull]

Originally Posted By: javacontour
One of the jobs of oil is to carry heat away from parts that are not water cooled. The lower the oil level in the sump, the same heat must be carried away by less oil.

I imagine it's easier to "vaporize" more oil in this circumstance, causing the problem to feed on itself.

Originally Posted By: KitaCam
yes Java...and my thought is, as oil level gets low, the engine is stressed even more, right (?) causing even more oil consumption...maybe.


Seems like there'd be enough headroom built in though that the cooling capacity of the oil would be sufficient at least for "normal" operation until you were *really* low. Most (all?) manufacturers don't technically recommend topping up until you are near or below the low mark on the dipstick, so I'd think that even at ~1 qt low the oil capacity would be enough to handle whatever the engine can dish out unless you're really flogging it.

Although stop+go in hot weather is probably the same as flogging it for the purposes of this discussion so maybe that does hold water in some situations.

 

[Hokiefyd]

The Cadillac Northstar engine was notorious for consuming oil rapidly if the owner kept it topped up to full or more. But if you let the oil level drop (or don't fill it passed) the "add" level, the engine won't consume a bit. The cause was crankcase windage: most of the oil when "full" would be consumed through the PCV system. But if the oil was "low", it'd ride along for many thousands of miles without budging a bit.

 

[javacontour]

The scenario I'm thinking of is once the oil is breaking down.

I agree, with new oil and a full to spec crankcase, there is headroom built in.

Now get to 90% into the OCI on a car that has a 3L crankcase capacity and the loss of 1 quart is about 30% of the oil.

I think there is a reason car makers list checking the oil level as a service done at every fuel stop.
Originally Posted By: rationull
Originally Posted By: javacontour
One of the jobs of oil is to carry heat away from parts that are not water cooled. The lower the oil level in the sump, the same heat must be carried away by less oil.

I imagine it's easier to "vaporize" more oil in this circumstance, causing the problem to feed on itself.

Originally Posted By: KitaCam
yes Java...and my thought is, as oil level gets low, the engine is stressed even more, right (?) causing even more oil consumption...maybe.


Seems like there'd be enough headroom built in though that the cooling capacity of the oil would be sufficient at least for "normal" operation until you were *really* low. Most (all?) manufacturers don't technically recommend topping up until you are near or below the low mark on the dipstick, so I'd think that even at ~1 qt low the oil capacity would be enough to handle whatever the engine can dish out unless you're really flogging it.

Although stop+go in hot weather is probably the same as flogging it for the purposes of this discussion so maybe that does hold water in some situations.

 

[KitaCam]

It's always interesting here...ask a question and get more information than you thought of asking for...

Letting oil drop to the lower end of the dipstick measure of "0" before adding is something I hadn't known....I always had topped off the level when it got half-way down the measure...I'll be more patient in the future...my current ride, kitacamry LE/i4 dropped a cup's worth @ 3k miles into the last OCI, so I don't think that's going to even be an issue...for now at least.

 

[rationull]

Originally Posted By: KitaCam
It's always interesting here...ask a question and get more information than you thought of asking for...

Letting oil drop to the lower end of the dipstick measure of "0" before adding is something I hadn't known....I always had topped off the level when it got half-way down the measure...I'll be more patient in the future...my current ride, kitacamry LE/i4 dropped a cup's worth @ 3k miles into the last OCI, so I don't think that's going to even be an issue...for now at least.


I tend to top off at 1/2 quart low too, FWIW. Just seems like most manuals call for topping off "at or near" the lower mark.

 

[Hokiefyd]

Consider waiting for it to get to the bottom of the safe zone. You may find that consumption slows as the oil level drops.