I’m curious, does the amount of oil in the engine sump/pan affect UOA readings? Example if your engine took 5 quarts, but it was a quart low(had only 4 quarts) when you pulled the plug to change the oil and grab a sample?
The correct answer is yes, no and maybe depending on the following. This question and scenario often come up in my ML-1,2 and LE trainings and its important in understanding the validity of a OA sample. Here's how this works.
A sump is a bowl and it collects "stuff". These particles ( the small ones are usually below 5 micron and often barely gram positive and some even almost colloidal)
There's no uniform mixer/agitator in an engine so there is no uniform distribution.
This it becomes the quality of the sample- is it truly representative of actual real time wear or am I sampling from a backwater (collection pond) or a rapid (excessively clean).
There is an art and science to installing sample ports in a machine then timing the sample to get a true working sample.
Samples drawn from sump drains and stagnant settled areas are notoriously skewed ( both ways- heavy and light)
Then there's the date stamp ( figuratively)- I got a particle count- is that last months particle? Is it new?
Another weakness when OA alone is used to attempt to monitor and measure wear.
Then come make ups- We document these in industrial lube programs because of the volume ( cumulative over time) combined with displacement and even making sure the make up oil is correct- this can irreparably skew additive data.
So the relative sump volume does have an impact but the measure of that impact depends on a lot of other factors.