Skewed UOA data

[Eddie]

I was looking at some of the conversations on taking UOA samples. I believe some of us maybe slanting (squing(sp) the UOA data by making an abnormally long run before taking a sample. If we do 90% short trips then we are running a fuel dilution of X% for the short trip. If we take the car out for a long highway run before the UOA then the data will yield a value that maybe considerable better than our usual value. I suggest that to get good data we need to warm up the engine by driving our usual daily run, be it 1,2 or 10+ miles.I think this is especially important for fuel dilution analysis. others thoughts? Ed

 

[JLTD]

Interesting thought.

I think "skewing" is the word you were looking for.

 

[SubieRubyRoo]

A couple longtime industry insiders have weighed in that fuel is not really a concern unless it makes the oil viscosity drop below the point it keeps metal surfaces apart. This level is unique to every engine type and how it is used; a 1.6 Chevy Spark may have problems at 3% dilution because the owner beats the snot out of it, while the Bugatti Chiron owner may have no problems at all at 10%+ because he never gets into the boost.

The viscosity will not significantly change from burning off a little extra fuel on a long highway run; I would personally be much more concerned about thickening from oxidation than I am about thinning from a little fuel. Why are people insistent on trying to draw corollaries where there are none? Just run your test the same way every time... if you like a highway run, do that. If you don't, don't.

But do it the same way every time so that your data actually means something; otherwise, just burn your UOA money because without consistency in test methods, there is no consistency to the results, either.

 

[Eddie]

skewing=yes thank you. Ed

 

[Eddie]

I disagree that do the UOA consistently any way you prefer. If we want accurate, as in-use data, then we want the data taken under real-use conditions. JMO.. ED

 

[MolaKule]

Suggestion:

Take a VOA sample of the current oil you are using before putting it into the engine.

Warm engine to operating temperature. Shut down engine.

Let cool until radiator hose can be grasped without burning hand.

For taking a sample for a UOA, take sample in "Midstream" which means take sample about a second or two after removing drain plug.

Look at UAO trends using the same oil before switching brands or types. Snapshots are virtually useless.

 

[doyall]

I do testing at select times during the interval to try to understand dilution accretion and abatement under various conditions. My findings - it happens quick with short-trip usage and does not significantly go away with a long-trip use.

 

[StevieC]

I've always taken my vehicles for a run until the oil is good an heated and then returned home and drained a sample within 20 minutes of shutting it down just to be sure I didn't skew the report in any way.
I usually plan to do shopping etc. before my oil change / sample and will go to the farther away Walmart / Costco etc. so it has a good decent run back.

 

[Eddie]

After reading all the comments regarding my original thoughts, I concluded, I may have over-thought the issue. However; it does seem to me that taking a longer than normal drive before oil sampling, puts the fuel dilution data in the most positive way. Ed

 

[MolaKule]

Modified the Title for You.

 

[Eddie]

Thank you MolaKule: Just couldn't think of the word Skewed so I substituted. Ed

 

[alarmguy]

Originally Posted by Eddie
I was looking at some of the conversations on taking UOA samples. I believe some of us maybe slanting (squing(sp) the UOA data by making an abnormally long run before taking a sample. If we do 90% short trips then we are running a fuel dilution of X% for the short trip. If we take the car out for a long highway run before the UOA then the data will yield a value that maybe considerable better than our usual value. I suggest that to get good data we need to warm up the engine by driving our usual daily run, be it 1,2 or 10+ miles.I think this is especially important for fuel dilution analysis. others thoughts? Ed


Your statement is true if you are just looking to see how your vehicle handles the oil that you use.
However your sample should not then be compared with other UOAs in the forum because your results are skewed/not taken in a standardized way using a controlled baseline to be compared with others.

SO wear metals are wear metals and comparable for sure but any comparison to viscosity/fuel should be completely ignored in reference to comparing to other UOAs.

 

[Eddie]

I was referring to the fuel percentage in the oil. If we take very long unusual drives to try to burn-off fuel, then the results may very well be different. That was my point to the original statement which got polluted by respondents. Ed