Someone set me straight on the PPM issue

[georgeyew]

On all of the used oil analysis that I've seen, the standard measurements are in parts/particles per million (PPM). These measurements are for particles that are too small to be filtered out. So are these measurements a good indication of wear since they do not take into consideration of the larger particles that have been removed by the filters?

I guess what I am saying is that an UOA with 6 ppm of iron, the oil would be considered great in terms of wear protection. But what if there were larger iron particles that were filtered out before the UOA?

Any thoughts?

 

[NewGuy]

Georgeyew....It is my understanding that ppm (parts per million) is a measurement of the % level of a particular product in the oil and NOT the size of a particle. 1% = 10,000 ppm.

In a sample with a given volume, if you have 2500 ppm of Calcium could be written as 0.25% Calcium in your sample. 6 ppm of Lead could also be written as 0.000006% of lead. Using ppms allows for easier communication and the very low levels aren't easily represented as percentages.

At least this is my understanding of how it works. My decimal places might be off, but I am sure that someone will correct me. Of course, I may be totally wrong.......

 

[georgeyew]

NewGuy, I think that you are correct in your understanding of ppm. But my question goes one level deeper. Think of it this way: someone is using a magnetic drain plug and it picks up some metal shavings from the oil. During the UOA, those metal shavings are not taken into consideration. If they were left in the oil sample, I am sure that the percentage level (ppm) would increase. Does that make sense?

 

[Scott P]

That concern also arose when discussing bypass filters. They filter/collect so well that they may disguise actual wear. I really have no clue which thread it was.

 

[georgeyew]

quote:

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They filter/collect so well that they may disguise actual wear

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Scott P, you explained my concern so well in so few words...I wish that I had that gift

 

[rugerman1]

quote:

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Originally posted by Scott P:
That concern also arose when discussing bypass filters. They filter/collect so well that they may disguise actual wear. I really have no clue which thread it was.

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bovine excrement

 

[pitzel]

Most often, what you see in terms of PPM are not 'particles' but rather compounds that have been formed of the various wear metals.

For example, wear iron becomes iron oxide, ie: rust, a substance that is very soluble in motor oil.

The underlying assumption we have to work from is that the amount of soluble metallic compounds generated from the use of the lubricating oil is somewhat in proportion to the rate of mechanical metallic wear within the engine.

However, it is entirely possible, due to certain situations, to have higher levels of iron, but still have oil that does not cause any accelerated rate of wear. For example, an engine left for 5 years without being run, inevitably will accumulate slightly higher iron due to corrosion. However, the byproducts of corrosion, by themselves, do not increase the abrasiveness of the engine oil, as they are mostly completely soluble, and the engine oil should still be, all other possible factors ignored (external contamination), suitable for continued use, despite a high iron level.

If one wants a true picture of wear in an engine, they really need to also be doing a filter analysis. We don't consider filter analysis on this website because they cost several hundred $$$ each, and most engines operated by people here are low-value engines, overhauled for not very much money.

The sort of used oil analysis done here are primarily useful for trendline analysis, and for determining lubricant life. Some lubricants might have absolutely horrible wear properties, but at the same time, also have horrible metallic solubility, thus giving artifically low numbers insofar as wear is concerned. For example, Esso XD-3 and Delvac-1, two extremely high-TBN/low TAN oils -- their extreme acid fighting and anti-corrosion additives might actually be more functionally useful insofar as producing good used oil analysis than their actual base oils -- without doing a filter analysis and engine teardown, we really don't know. (well we do actually know since people have done XD-3 and D-1 teardowns and they come out excellent).

 

[Ugly3]

quote:

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Originally posted by georgeyew:
On all of the used oil analysis that I've seen, the standard measurements are in parts/particles per million (PPM). These measurements are for particles that are too small to be filtered out. So are these measurements a good indication of wear since they do not take into consideration of the larger particles that have been removed by the filters?

I guess what I am saying is that an used oil analysis with 6 ppm of iron, the oil would be considered great in terms of wear protection. But what if there were larger iron particles that were filtered out before the used oil analysis?

Any thoughts?

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There is very little if any data that demonstrates the PPM of wear metals in a used oil analysis is representitive of the actual wear in an engine.