Are wear metals expressed in ppm/1k miles meaningful numbers

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Jun 26, 2003
LA (Lower Alabama)
I've seen quite a bit of comparisons and analyzations of UOA's using ppm/thousand miles for wear metals. I understand the concept of reducing things to a common basis to account for number of miles used differences in order to make a comparison, but can the wear metals in oil that has been run 3,000 miles really be compared to wear metals in oil that has been run 6,000 or 9,000 miles to conclude that oil "S" performs better than oil "D" all things other than miles used being equal? In other words, can 10ppm/1000 miles over a 3,000 mile interval really be considered inferior performance to 5ppm/1000 miles over a 9,000 mile interval? [ November 18, 2003, 03:23 PM: Message edited by: doyall ]
My take on it is that it's a rough guide, but not exact. Here's why. If you've got an oil which has 5ppm of any given wear metal in it's virgin state, and then you run it for 3000 miles, and add 5ppm more, you'll show a much higher wear (in ppm/1k) compared to if you ran that same oil for 6k. Example: new oil has 5ppm of iron You run it for 3k and end up with a total of 10ppm of iron, so you're average is 3.33ppm/1000 miles. But if you run that oil for 6k, and wear continues at the same rate, and you end up with 15ppm of iron, the final number is 2.5ppm/1000 miles. So the numbers look higher on the shorter intervals, but not because the actual wear is higher. You also need to remember that when you put in fresh oil, in some engines there can be as much as one quart (or more) of oil left behind, and it obviously mixes with the new oil. So if you sampled it right away, you'd see some wear metals in it already. So in other words, the lower your interval, the less accurate a picture you'll actually get in terms of wear per 1000 miles. It is best used if comparing similar intervals, such as one 5k run to a 7k run for example. Not to compare a 3k run to a 10k run.
In general I believe that it is a fair comparison for wear metals. It obviously helps to know if some of those wear metals are present in the virgin oil but as wear should occur over time, in theory then I would say that it is a fair comparison. Now, driving conditions could play a factor but if we keep things equal yes. I also feel that these wear metals, iron for example, are too small to cause additional wear so 10 ppm at 3000 miles is the same as 33 ppm in 10,000 miles. Now, silicon is another matter and most labs use an absolute rather then a relative scale for this, 30 or so ppm may be a cut off point for flagging the oil to be changed by some labs (other then maybe a new engine). However, above all else the trend is the most important factor in any program. As long as the trend for wear metals is moving down or staying the same I feel that life is good.
I believe it is relative, maybe not exact, but the trend tells you things are going right or wrong. Not on the first sample as stated. I've run 9,000+ hrs on side by side equipment, one showing about 9 ppm iron and the other 23 on each sample, consistently throughout the 9,000 until the one engine gave out.
Originally posted by doyall: I've seen quite a bit of comparisons and analyzations of UOA's using ppm/thousand miles for wear metals. -*-*-*- In other words, can 10ppm/1000 miles over a 3,000 mile interval really be considered inferior performance to 5ppm/1000 miles over a 9,000 mile interval?
Plot it on a graf. Wearcheck has one of iron, Aluminum, copper, Lead, Silicon (on the second sheet)... Over time you WANT to SEE the LINES all staying flat, or moving downwards... you do not want to see spikes... you do not want to see metals like lead or contaminations like SIlicon going and staying over the bottom line they use as a marker (named Abnormal), you want to keep all the levels as flat as you can, and when one spikes like SI, then you must take some corrective action to level it back again, which is not right away because it could take a OCI or two. You are looking for levels, but you are also looking for trends. The real deal, is IMO, to watch over time the results and notice what the metals and the contaminates do, how they bounce around, and learn to predict what they will do before they do it on their own, and take action before it happens. Easier said than done.
I think it is also a rough, but useful measure of differences between oils. Here are some comparisons of various brands I calculated using the ppm/1000 mile approach:
       M15W30 Am0W30 GC0W30 GTX5W30 Chev10W30
Fe,     3.25   1.78    2.57   1.53    1.38
Cr,      .25    .23     .08    .19     .0
Pb,     2.64   2.47     .51   1.25     .48
Al,      .91    .69     .35    .84     .48
Cu,     1.48   1.56     .77    .86     .86
Sn,      .27    .09     .16    .09     .19

People frequently say general things like, this oil is better than that one, or we've seen good UOA numbers on that oil. So I did a search of a number of UOA reports to line up the oils I was interested in comparing and came up with these figures. It was a handy way to normalize the data along one parameter since no one else in the world is smart enough to change their oil at the same duration I do. [Roll Eyes] Someone else selecting different UOA reports (or different selection criteria, or sample size, etc.) will obviously generate different numbers that could very well change (or verify) my lineup. I'm not advocating one oil over the other. My point is simply that this can be a useful tool to keep in mind along with all the other factors one considers while searching for that oil which best fits their car. [Smile]
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