Originally Posted By: fdcg27
Originally Posted By: MolaKule
Originally Posted By: Red91
I've read quite a few threads on here about more frequent oil changes causing more wear due to the fresh oil washing away the anti-wear layer put in place by the old oil, but how realistic is this theory?...What say you?
I don't think there is any real data to support that other than a few inferential comments from papers whose authors wanted some limelight as if they had discovered something new.
Consider this about an oil change:
1. fresh oil carries a new additive pack that replenishes the additive components (that have been degraded) including the detergent and Anti-Wear components,
2. replaces oxidization byproducts and the contaminants that were previously there.
IDK
Dave Newton showed pretty conclusively that wear rates were lower per thousand miles on longer drain intervals.
OTOH, I ran many engines for many thousands of miles on short 3-4K drains long before I even considered UOAs or wear rates. There is an old-school philosophy that an engine will last just about forever if given plenty of fresh, clean oil. Seems like common sense.
The data as presented by D. Newton don't really support that notion, though.
Dave Newton didn't prove anything. He has no data that was controlled for the variables discussed below. Of course he never returned to the thread for any discussion of how he had controlled those variables.
Quote:
Originally Posted By: dnewton3
I'm not inflating anything. My data analysis is fair and accurate.
I am open to any discussion based upon facts and credible study (not conjecture or theory) that would counter mine.
Let's start with your data. We'll deal with the SAE article in separate posts.
Your data is Blackstone UOA, correct?
Do you have VOA's for each of the data points you use? It's necessary to subtract any wear metals present in the virgin oils, as any present effect your results.
I've given the following alternate explanation for higher wear metals at lower mileage in the past. It's a valid phenomenon that may explain part or all of what you see in a simple UOA. The "blip" we see in UOAs can not be used to demonstrate this supposed phenomenon either. Carryover is an uncontrolled variable.
Let's take an engine with a 5 qt. sump with 10% carryover that produces a constant 10ppm Fe per 1000 miles, and a 10K OCI as an example. Draw a sample at 1 mile and at every 1K thereafter. This is what the data would look like:
1 mile 11 ppm = 11ppm/mile
1K miles 21 ppm = 0.0210 ppm/mile
2K miles 31 ppm = 0.0155 ppm/mile
3K miles 41ppm = 0.0137 ppm/mile
4K miles 51 ppm = 0.0128 ppm/mile
5K miles 61 ppm = 0.0122 ppm/mile
6K miles 71 ppm = 0.0118 ppm/mile
7K miles 81 ppm = 0.0116 ppm/mile
8K miles 91 ppm = 0.0114 ppm/mile
9K miles 101 ppm = 0.0112 ppm/mile
10K miles 111 ppm = 0.0111 ppm/mile
There you go, higher wear metals seen in shorter mileage UOAs explained by simple math, no extra wear required.
Have you determined the extent of this phenomenon for every engine and application in your data set and corrected for it? If not you can not say that the increased wear metals is from wear.
Have you done experiments to determine if the higher metals might be from fresh oil solving varnish and sludge an releasing precipitated wear metals back into the oil? Unless you have proof that this is not a factor, you can't claim the higher wear metals are from wear.
How are you distinguishing metals present from wear vs entering the oil by other mechanisms, such as corrosion? The first rule of analytical chemistry is that if you are going to analyze for iron, don't store the sample in an iron bottle.
The big elephant in the room is that UOA by ICP is not a proxy for wear. The limits of the instrumentation prevent it from being used as such. It is possible to have "high" wear metals and lower wear than an engine with "low" wear metals. What supporting proof do you have for each data point that is is a valid indicator of wear? An example would be ferrographic particle counts, or measurements of each engine correlating actual wear with the UOA data.
Now, let's talk about the size of those particles that make it into the plasma. You've probably read many times that ICP can see wear particles at about 5 microns. The labs will tell you this also. They are wrong.
The particle size is based on the aerodynamic diameter, not the actual diameter. An ICP is designed to have a hard cut off of 4.5-5.0 microns due to the fact that droplets larger than that destabilize the plasma. That's where the 5 micron figure comes from. The problem is that is the aerodynamic diameter and is based on a spherical droplet of water. Aerodynamic diameter is affected by density and shape. Metals have a higher density than water, therefore smaller particles are required to achieve the same aerodynamic diameter and be allowed to pass through to the plasma.
This is one of the many reasons why "wear metals" do not serve as a good indicator of wear. The ICP only sees a portion of "normal" wear and miss most if not all of the larger particles generated by abnormal and break-in wear. The other is that due to the different densities of the metals the instrument does not see them equally. Given an equal amount and distribution of particle sizes, the ICP could read 4X as much aluminum as lead due to the density difference between the two. An accurate measure of what is in the oil can only be made if the oil undergoes a digestion to put the metals in solution.
The first 5 pages of this presentation cover what I have talked about. The illustration at the top of page 5 shows the relationship visually. They use a material with a density of 4000 kg/m3 for illustration. Aluminum, depending on alloy has a density of about 2700-2800, copper 8940, iron/steel 7850, and lead 11340. Visualize the 4000 kg/m3 circles at half that size and that is roughly the relative size of an iron particle that an ICP can see vs the 4.5 micron water droplet.
Aerodynamic Diameter
Ed
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Never attribute to engineers that into which politicians, lawyers, accountants, and marketeers have poked their fingers.