Oil Level Change Weirdness

[ZeeOSix]

The two graphs below are oil use rate data of two oil fills. Oil in both crankcase fills is Motorcraft 5W-20 synthetic blend.

There was no measurable oil use for the first 400~500 miles in each case, so no data in the graphs until around 500 miles when the oil level starts to change on the dipstick and the use rate is calculated. Oil level was always checked in the same spot (garage) and when cold for consistency. Oil dipstick has hash marks which I use as a scale for the oil volume change at each level check.

Notice how the oil use rate goes down (ie, a higher miles/qt number) around the first 600~700 miles on the oil, then settles down to a pretty constant rate with about 1000~1200 miles on the oil. This happened with both fills, so it looks like a repeatable trend.

Plan on using a different oil next oil change, so will be interesting to see what the use rate graph looks like for that particular oil.

Thought it was kind of interesting. Anyone have an idea why this happens? Most volatile components burning off, then settling down? Shearing causing more to get by the rings? Don't think there's any real fuel dilution on this engine (NA with PFI, non-DI).

Oil Fill #1
Factory fill. No oil use seen for the first 400~500 miles, so no curve data.


Oil Fill #2
Oil changed at 2200 miles. No oil use seen for the first 400~500 miles, so no curve data.

 

[OilUzer]

I have noticed many times that oil burns off (or evaporate?) quickly the first 400-500 miles and then settles ... but your charts showing different. Basically not much loss the first few hundred miles!
What is the y axis?

 

[Danh]

So, if I’m interpreting correctly, you were able to detect consumption of 1/30 of a quart at the 500 mile mark by reading the dipstick?

 

[ZeeOSix]

Originally Posted By: OilUzer
I have noticed many times that oil burns off (or evaporate?) quickly the first 400-500 miles and then settles ... but your charts showing different. Basically not much loss the first few hundred miles!
What is the y axis?


X-axis is miles on the car. Y-axis is the oil use rate (miles/quart).

 

[ZeeOSix]

Originally Posted By: Danh
So, if I’m interpreting correctly, you were able to detect consumption of 1/30 of a quart at the 500 mile mark by reading the dipstick?


The dipstick has 6 hash marks between the "Add" and "Full" lines (which equates to 1 qt), and I can estimate the level to the nearest 1/4~1/5 division. That gives an estimated resolution of around 1/30 of a quart. Always measured cold and in the same parking spot in the garage. It at least gives a repeatable way to measure a trend as the graphs show. If it didn't there wouldn't be this much of a trend between the two graphs. I'm looking at a trend here, not data to the Nth degree of accuracy.

 

[CT8]

What exactly are we getting at ? Miles per Qt?

 

[ZeeOSix]

Originally Posted By: CT8
What exactly are we getting at ?


Why does the oil use rate change drastically until there's around 1000~1200 miles on the oil, then settle down to a constant rate.

Like said earlier, will be interesting to see if a different oil produces a different curve.

 

[OilUzer]

FYI
I asked a question regarding oil burning off or evaporating quicker in the first 500-1000 miles ...

From MotoTribologist (sp?):
"Evaporation rates generally start high and level off over time as less and less volatile material remains in the bulk of the oil due to said evaporation."

however your observation is different!

 

[CharlieBauer]

Be much easier to understand the graph if the y axis was oil qty. Then have two curves. 1 for oil level and 1 for oil consumption.

 

[ZeeOSix]

Originally Posted By: CharlieBauer
Be much easier to understand the graph if the y axis was oil qty. Then have two curves. 1 for oil level and 1 for oil consumption.


The oil consumption (miles/qt) is based off of the measured oil level, so it doesn't give any added info if the oil level was shown. The miles/qt use rate curve is showing that the change in oil level goes way down (stabilizes) after about a 1000 miles on the oil.

 

[ZeeOSix]

Originally Posted By: OilUzer
FYI
I asked a question regarding oil burning off or evaporating quicker in the first 500-1000 miles ...

From MotoTribologist (sp?):
"Evaporation rates generally start high and level off over time as less and less volatile material remains in the bulk of the oil due to said evaporation."

however your observation is different!


Maybe due to more than one thing going on at the same time in the first 1000 miles.

 

[UncleDave]

Curious to see where this may go.

Ive noticed similar "non linear" post OCI consumption effect on my diesel genset but not my autos.

UD

 

[OilUzer]

Originally Posted By: ZeeOSix
Originally Posted By: OilUzer
FYI
I asked a question regarding oil burning off or evaporating quicker in the first 500-1000 miles ...

From MotoTribologist (sp?):
"Evaporation rates generally start high and level off over time as less and less volatile material remains in the bulk of the oil due to said evaporation."

however your observation is different!


Maybe due to more than one thing going on at the same time in the first 1000 miles.


Actually the later part of your observation (based on your charts), is same as what MotoTribologist was saying as far oil burning "leveling off" ...
The first part of your graph (the hump) however may not look very conventional and looks inverted. This is based on my experience but I never collected this level of data & details.

 

[Triple_Se7en]

1) How long does it take you to accumulate 500 miles?
2) How many times per week do you check the oil?
3) We would like to know how many times you wipe-off that dipstick, during that 1/30th of a quart loss?

 

[Gokhan]

I had exactly this behavior when my engine used to consume a lot of oil (before I replaced the valve-stem oils).

I didn't pinpoint the cause but my primary suspect was the nonlinearity of the dipstick. Chances are that right above the full mark, the sump widens a lot and the level doesn't rise or fall as fast.

Try this: When you top off the oil and when you change the oil, bring the level to the exactly the same spot on the dipstick every time but never past the full mark. If the nonlinear behavior goes away when you do the measurements, you pinpointed the cause. It's crucial for this verification to work that during the oil change, you don't go beyond the full mark even a bit.

If it doesn't, then the used oil is consumed faster for some unexplained reason.

Looking at your graphs again though, since you say "no oil is used in the first 500 miles," I am fairly sure that it's the nonlinearity of the dipstick combined with too much oil being put in during the oil change -- the oil is always being consumed at more or less the same rate but you're not seeing it in the first 500 miles because of some systematic error that has to do with (1) too much oil being put in initially during the oil change and (2) the nonlinear part of the dipstick above the full mark, which doesn't show the overfilled amount of the oil properly. Again, I had very similar behavior and this was probably the correct explanation.

 

[ZeeOSix]

Originally Posted By: Triple_Se7en
1) How long does it take you to accumulate 500 miles?
2) How many times per week do you check the oil?
3) We would like to know how many times you wipe-off that dipstick, during that 1/30th of a quart loss?


1) Varies, average of maybe a month. Not a daily driver.

2) The data points on the graph indicate each oil level check point.

3) Once. I check the level cold, so only takes one wipe. Besides, 1/30 of a quart is a little over an ounce, which would probably take over 100 wipes or more of the dipstick to equal.

 

[ZeeOSix]

Originally Posted By: Gokhan
Looking at your graphs again though, since you say "no oil is used in the first 500 miles," I am fairly sure that it's the nonlinearity of the dipstick combined with too much oil being put in during the oil change -- the oil is always being consumed at more or less the same rate but you're not seeing it in the first 500 miles because of some systematic error that has to do with (1) too much oil being put in initially during the oil change and (2) the nonlinear part of the dipstick above the full mark, which doesn't show the overfilled amount of the oil properly. Again, I had very similar behavior and this was probably the correct explanation.


There definately wasn't too much oil put in at the oil change. In both cases the oil level started right in the "Full" line on the dipstick.

I've also verified that the level volume between the "Add" and "Full" mark is exactly 1 quart.

It could be dipstick non-linearity, I haven't checked to verify. I wouldnt think it would be that bad if it was non-linear.

Like said before, will be interesting to see if using a diffetent oil (Valvoline 5w30 Advanced) shows a different graph result.

 

[Gokhan]

Perhaps you can try filling to a definite level around 3/4 between the add and full marks at the next oil change and then do the rest of the measurements and top-offs at that lower level, instead of the full mark. This could better identify any nonlinearity with the dipstick.

 

[ZeeOSix]

^^^ Next oil change (probably in September) I'll try to verify the dipstick linearity between the "Add" and "Full" marks. I'll fill with new oil to right on the "Add" mark when cold, then add 8 oz at a time (and wait an hour between adds) to see if the level change is linear on the dipstick.

I want to start monitoring oil use from the "Full" mark using the Valvoline to be consistent and, see if I get the same graph shape trend.

 

[Gokhan]

Originally Posted By: ZeeOSix
^^^ Next oil change (probably in September) I'll try to verify the dipstick linearity between the "Add" and "Full" marks. I'll fill with new oil to right on the "Add" mark when cold, then add 8 oz at a time (and wait an hour between adds) to see if the level change is linear on the dipstick.

I want to start monitoring oil use from the "Full" mark using the Valvoline to be consistent and, see if I get the same graph shape trend.

Actually, this is a very good idea. There is probably no need to wait that long. I would do 4 oz at a time with five minute waits in between and then plot the entire add-to-full region. You can even keep adding above the full mark to see where it takes you. If you have the Blackstone vacuum pump (something everyone should have for UOA's), you can then remove the excess oil. It uses 1/4-inch polyethylene tubing to go into the dipstick tube. Or siphon out the oil using some tubing after you start it off with the vacuum pump or a syringe held close to the ground.

Blackstone vacuum pump