Confusing UOA's D1G2 PP 5w20 mix in '18 5.0L Ford

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Individually, none of these UOA's is particularly interesting. My confusion is between test 2 and 3 which was the exact same sump of 50% PP 5W-20 and 50% PP 5W-30, all D1G2.

Test 2 was after apx. 6 months of mostly typical short-trip driving - 2 or 3 or 4 miles per trip. Sometimes even 10 miles per trip.

Test 3 was after a four-day road trip and was taken immediately after the 210 mile drive home with 2 intermediate 10 minute stops. (The purpose of he test was to see if fuel dilution would decrease with a lengthy drive.)

Otherwise, the same protocols were used for both tests.

One of the things that confuses me between test 2 and test 3 is the difference in reported levels of magnesium, phosphorus and zinc. Depending on which way you cypher it, there is a reported difference of between 13% and 18% in these elements. Seems to be outside of an acceptable margin of error to me. I would tend not to be concerned about something less than 10%, but maybe I am overly optimistic. Any thoughts?

More confusing is the viscosity reading of test 3. When virgin my 50/50 mixture should have been somewhere in the 9.2 cSt @ 100°C based on typical viscosities from the data sheets. Test 2 with 3.4% fuel seems to be in the realm of a correct viscosity at 7.8. If my 210 mile trip did in fact evaporate enough fuel to warrant a 2.3% level (I am skeptical) I would venture to estimate the viscosity should have been somewhere around 8.2 to 8.3, not the 9.2 reported. I am at a loss to fathom how oxidative thickening or some other phenomenon could have increased the viscosity that much over that little time and usage. What could I be missing?

11-13-18-truck-uoa-2&3.jpg
 
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There does seem to be too much measurement error for the small 210 mile difference between samples 2 and 3. It's not uncommon. When there is a large difference in miles, the real deltas are not overwhelmed by the measurement errors.
 
This is a perfect example of how variation must be understood PRIOR to making conclusions.
There is variation in the lubes, the samples, the tests, the lab personnel, etc ...

Ever read this?
https://www.bobistheoilguy.com/used-oil-analysis-how-to-decide-what-is-normal/
Understanding what is "normal" means you first have to understand how much variation exists at every point in the whole process. There is, most certainly, variation in the testing equipment and personnel (typically called Gauge Repeatability and Reproducibility; aka R&R for short). Then on top of that there's variation in the samples, from the normality of life's variable inputs.

Only one of three things can be stated as true regarding these UOAs and your questions:
1) the tests are completely accurate, indicating that sumps vary a LOT in VERY SHORT cycles
2) sumps are steady, and test variation is MUCH larger than folks believe
3) some combination of the two above
We could eliminate #2 and also #3 by running a gauge study. I've offered to run a study on the accuracy of some labs, but no one has stepped up to help finance the project, as it would not be cheap for me to pay for personally. Oddly, with over 65,000 members here, we cannot seem to come up with $1000 of donations to do it the right way.

As for the UOAs themselves, there's nothing alarming here. Even though the data does not make complete sense to you, the magnitude of values shows nothing to worry about. After all, 3 UOAs in 4.2k miles is a bit overkill. The only thing you're learning is that you cannot put too much faith into a process you don't fully understand due to variability.
 
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Originally Posted by BMWTurboDzl
OP, You're wasting $$ on UOA's. Put down the sampling bottles, relax, go spend the weekend at the Beau Rivage


Thank you for your "concern" over my state of being but rest assured I am not frantic or in any other condition from which I need to relax. Looking for clarity is a far cry from being frantic. As far as wasting $ ($$ seems hyperbolic), as long as I am obtaining information beneficial to me about my equipment under the conditions in which it operates, I do not consider it a waste. (Even if the information I got from test #3 is only about the lab, it was nonetheless beneficial.)

If you want to provide useful information, please share with me where I can get a fuel dilution test using gas chromatography done for less than the meager cost of a basic, bulk-purchase Polaris UOA.
 
I also use Polaris Labs. On one occasion I had a suspect sample report. I contacted them and they were able to re-run the sample, so evidently they keep the samples for a brief period of time. It's worth asking them.
 
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