corrosion vs friction

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Jan 29, 2006
First, I am not coming to any conclusions based on data of unknown (to me) origin. But I have looked at a data set that has left me with a question. Background: In another thread, "1sttruck" is attempting to use a data set (origin unknown to me) to derive conclusions about viscosity and wear. I collect, analyse, and publish data for a living. So, I thought I would download the data set and "have a look". Excluding the obvious issues with unknown confounding parameters, the first thing that I noticed is that the Fe and Al numbers are not a good fit to a model where wear of these metals is linear with miles traveled. The transformation of the data as "miles per unit metal" is therefore not valid. Observation: However, the Fe and Al are highly correlated with each other. It is my impression that Fe and Al would rarely be found as opposing, moving surfaces. So, what factors would make Fe and Al climb together? I am left hypothesizing that maybe corrosion (however small) is the main source of these metals in used oil. I have found several references for marine oil usage that suggest that corrosing is the main source of "wear" in those applications (maybe as high as 90%). Does anyone know if corrosion could be the main source of wear in the average auto? If so, then lubrication would not be the current weakness in oil. Instead, the current weakness would be inhibition of corrosion. This situation would change the way that I think about oil. Any thoughts? Facts? Feel free to blast me if I am way off base. I would think that a good tribologist would have a well established answer for this issue.
Originally posted by GMorg: It is my impression that Fe and Al would rarely be found as opposing, moving surfaces.
No blast intended, but it's common practice to mate ferrous camshafts directly to the machined bearing journals of aluminum cylinder heads. Aluminum pistons are mated directly to cast iron blocks and ferrous cylinder liners. The rule for moving surfaces is always a hard metal mated to a softer metal. What you won't find are identical metal moving parts mated directly together - iron/iron, aluminum/aluminum*, etc. because of their tendency to weld themselves together. Momentary oil film loss leads to early wear in this instance. In the case of the cheapest consumer-grade air-cooled utility engines which rely on splash lubrication systems, chrome-plated aluminum pistons with iron piston rings are mated directly to the machined aluminum cylinder bores, yet if given a yearly oil change, these engines can last over a decade. *GM pioneered mating aluminum pistons to high silica content aluminum unsleeved blocks in the mass-produced Chevy Vega engine. After the block was machined, the cylinders were acid etched to leave a hard silica "liner" that the piston rode in. While Vegas had premature cylinder wear problems, the technology was eventually tamed to provide reliable service. [ February 15, 2006, 11:56 AM: Message edited by: Ray H ]
Ray H, Good points, but shouldn't the softer metal appear in the oil at a faster rate than the harder metal. [Confused]
"...the first thing that I noticed is that the Fe and Al numbers are not a good fit to a model where wear of these metals is linear with miles traveled. The transformation of the data as "miles per unit metal" is therefore not valid." Look at earlier threads on UOA vs wear for starters. There are at least a couple of things going on here: 1. Something that I see a lot with people trying to draw conclusions from data is that fitting some sort of best fit line thru the data is kind of like a trap, as if it's the only way to look at data. Some data sets exhibit lots of scatter but stepping back and looking at it there are still boundries which beg for some sort of inequality, where one can make statements about a boundry that defines the data set. Otherwise you need to come up with a way to handle extreme values, where a log transformation is common, exclusion, etc. 2. A big problem with statistics and modeling are the unstated assumptions, and a big one here is that ppm of metal in a UOA correlates with wear. I wasn't satisfied with that assumption, and looking into it I've become comfortable with typical UOAs being useful for the state of the lubricant, but other methods are needed to try to determine wear. That's why UOAs son't seem to used for wear analysis, although they're still very useful for detecting some problems as part of a maintenance program. To use UOA for wear I think that you need to: a. Clean the engine very well. b. Run the intended oil with at least one flush. c. Do the test, collect the data, including mass estimates from particles in the oil as well as in the filters. d. Clean the engine very well and collect the fluid for estimating metals that may have remained in the engine.
According to my conversations a few years ago with the technical contact at one of the oil companies often discussed on BITOG, at least a good amount (most? I cannot say) of the 'wear metals' present in a UOA are a result of the reaction of the metals inside the engine with a new oil fill (add pack components, bases, everything), and not of actual wear. I believe this is in fact the case and it would explain why the relationship between miles run and ppm of some 'wear metals' do not correlate well at all. I believe it also explains why you can sample an oil at 750 miles and again at 1500 (even 2-3K perhaps) and see essentially the same ppm levels of those certain metals. Terry Dyson has commented here before that some wear metals' concentrations do not increase linearly wrt mileage. This agrees with the assertion above. IMO this is one reason why so very many of the UOAs at this site are not useful for comparison at all; the oils analyzed have not been in service long enough to pull wear trends out of the background reaction levels. Sadly, the levels seen in these short OCIs could be 'interpreted' (not genuinely interpreted by people like Terry Dyson, rather by laymen like me and most all of the rest of us) as showing that one oil is superior to another wrt wear protection when in fact all that is visible is the level of reaction between that oil formulation and the engine internals.
Even Exxon has stated that when using one of their synthetic blends for aircraft that one will see elevated wear metals for awhile, as does Royal Purple. There is a lot of surface area inside of engines, some anti-wear additives seem to incorporate available metals during film formation, and sludge/varnish forms to some degree over time, where it is reasonable to assume that those films also have some wear metals in them. The wear metals in a typical UOA are an unkown portion of the total wear metals in an engine, due to what has been incorporated into films and what has been picked up by the filter. It'd be nice to see a 'Rosetta stone' study, where UOAs, radioactive trace of wear, and tear downs are performed in an attempt to correlate everything.
Fe in cylinder wall and piston skirt are one example of sliding surfaces. I copied this from bob's front page: "Aluminum (Al): Thrust washers, bearings and pistons are made of this metal. High readings can be from piston skirt scuffing, excessive ring groove wear, broken thrust washers, etc." I agree that a lot of data has shown that wear is not linear with respect to miles and that therefore calculating ppm/miles is only relevent when comparing similar mileage intervals. And just yesterday I was thinking of making a thread to discuss why. The only explanation I can think of is that younger oil's higher TBN causes more wear metals to show up in the UOA, whether it be from true wear or from cleaning of metal surfaces. Also, esters (like Redline) seem to usually put more wear metals in the oil and that could very well be from it's cleaning powers, and not true wear, since it's anti-wear additive package is very robust. But I can't prove that Redline isn't actually unable to prevent corrosion and that's why the UOAs look as they do. I know different basestocks have different capabilities to prevent corrosion, so it does make me wonder, but on the other hand, there are anti-corrosion additives as well. I use a magnet inside my oil filter that I can inspect/clean after each oil change. There are iron particles on it and I've looked at them under a microscope as well. They are not corrosion compounds (oxides). So true wear certainly does occur in engines. At this point, I think that cleaning the metal surfaces is a good thing (whether from additive package or ester basestocks), even if it causes wear metals to show up in the UOA, because I don't think there is large scale removal of material/dimension change on parts. I believe wear does cause large scale material removal/dimension change. Keeping the metals clean should help the anti-wear additives do their job better by having access to bare metal. Even more important perhaps is an oil cleaning the ring packs which will help them seal, allow oil to reach the upper cylinder, but scrape off the excess oil as well. This is much along the lines of the theory behind Auto-RX. This is just my opinion at this time and I am open to other ideas. Motor oils do contain anti-corrosion additives already, so the formulators are on top of that issue. What I'm calling cleaning is different than corrosion but they both cause wear metals to show up in the UOAs and neither is a result of wear.
Originally posted by GMorg: Good points, but shouldn't the softer metal appear in the oil at a faster rate than the harder metal.
Amazingly, no, unless there're serious amounts of abrasive contaminants and/or acids present. Even steel or iron crankshafts ride on soft metal - the lead-containing babbit alloy applied to the steel main bearing shells. Dissimilar metals are self-lubricating to some degree since they resist welding together. Add a reliable oil film and half decent* filtration, and 300,000+ miles isn't beyond reason. *as in two-dollar SuperTech or Valuecraft oil filters (shoot, look at the number of drivers who're making Honeywell Systems rich and still getting by just fine on three-dollar FRAMs [Eek!] ...) [ February 15, 2006, 12:39 PM: Message edited by: Ray H ]
I just want to add one more thing. I plan on doing some tests with different motor oils, putting a corroded penny into a cup containing motor oil at 212F degrees to see if/how long it takes the oil to remove the copper oxides. If it isn't able to, I can modify my theory that motor oil can clean oxides off of at least some types of metal surfaces given enough time. I should probably test an ester based motor oil as well to get the whole picture.
As promised, I started the corroded copper penny tests last night. I put the corroded penny into a metal cup containing Syntec 5W-40 oil at around 212F degrees for several hours. Result: no change in color of penny - no significant removal of copper oxide coating. I am going to continue the test and see if it just needs more time and also see if wiping the penny with a q-tip will easily remove the corrosion (maybe it's "loose" but still there). If even that fails, I'll move on to different oils and may even order some Auto-RX and put some of that in and see how that does. I must say I am disappointed in the result so far considering that you can rub car wax on a corroded penny for a few seconds and the oxide layer comes off easily. So far, typical motor oil sure is looking like a weak metal cleaner.
GMorg, that's awesome that we are doing similar tests. We can help each other by sharing info. The penny I used is a brown (oxide) penny. Your tests are interesting because of the propensity of esters to absorb moisture. I know you had a thread about that and Molakule chimed in. It might require high temps and very high humidity which unfortunately is a lot harder to test than putting it in the shower. Since I no longer have Redline oil and don't yet have Auto-RX, if you are interested in doing it, could you also do a test like I'm doing but with Redline and Auto-RX to see if they can remove the brown oxide coating on a penny? You'll have to somehow heat the oil and keep it around 200F or higher. One way is to put a little metal or pyrex glass cup over a candle; another is to put the cup on top of a strong light bulb (>75 watt) that is meant for portable use like a light to hang over your engine while you work on it (Lowes sells them). If you can't or won't do this that's okay, but I figured I'd ask. If Redline and Auto-Rx can't do it, I don't think any oil can. A while back I did some other corrosion tests where I whiped new motor oil on a one half of a steel plate and left the other half bare. Then exposed the plate to humidity to see if the oil could prevent rust on the part it was on. It could NOT! I was shocked.
JAG, I'll try to set it up this weekend with Redline 5W30 and AutoRX. I am not expecting much with just a few hours, but if I see something I'll repeat with a greater selection of oils. I have access to equipment to control temperature within 0.1 degrees C but I am limited to about 205.
That was very interesting. Those rusty pieces of metal in some of those pics look my rusty plate looked like. I can't remember what oil I used on my steel plate but I know it was synthetic and it sure didn't do well at preventing rust. I would have thought that good motor oil would be better at preventing rust than that. The article said the anti-rust additive is a polar molecule that temporarily bonds with the metal - I didn't know that! Thanks for the link.
Jag, Are you using a brown penny (oxides) or a green penny (Cu sulfide an sulfate)? I currently have Redline and AutoRx on brown pennies and new, shining pennies. However, I am looking for moister effects. The oiled coins are in may bathroom near the shower. No direct splash, but high humidity. I am curious if the ester based fluids will accelerate oxidation in the presence of moisture. They have been in place for about two weeks and haven't changed a bit. Even the uncoated pennies are unchange so far. The two oils are protecting the pennies just as well as far.
JAG, I ran your experiment this morning. I placed 3 microliters of Redline 5W30, AutoRx, or Havoline 5W20 onto Lincoln's lap (sitting in the monument) on the back of tarnished, pre-1983 pennies (penny composition changed in '83). The three pennies were held at 210.2 degrees F (99.0 C) for one hour. At the end of 1 hour, I could not tell any difference between the pennies. I use a white paper towel to wipe the pennies clean before I placed them back into my pocket. To my surprize, the Redline and Havoline produced clearly green stains on the papertowel. The AutoRx is so dark anyway that I cannot say it was or was not green. The pennies however did not look any different than before the test. Actually is used such a small volume so that the oil-less edges of the Lincoln monument could be used for direct comparison. To make sure that I was not looking at a natural color of the oil, I rubbed (with my finger) a small amount of each oil onto the fronts of the same pennies and then blotted them clean onto the same paper towel. The starting material was not green and did not become green when exposed to the pennies at room temp for a short period of time. So, either heated Redline and Havoline turn a little green when heated or something was removed from the penny. Since the pennies were the normal brownish oxide and generally green from copper is likely Cu sufate, sulfide or cloride, I don't really know what to conclude. My wild guess is that part of the add pack may be attacking/displacing the copper. This experiment was not sufficiently controlled to come to any conclusions! This could be due to salt from my hands on the pennies! Please don't jump to any conclusions, please! I will think about repeating the experiment with uniformly oxidized copper plate or wire that is also cleaned of surface contaminants. I would also use a non-metalic substrate to heat the oils in parallel.
Thanks a lot for the tests! So far the ability of motor oils to clean corrosion off of copper looks to be very weak. I held hope that Redline and especially AutoRx would make a huge difference from my Syntec 5W-40, but it doesn't seem that way so far. I am starting to think that maybe what we are seeing is a good thing though. If oils could strip a penny in such a short time, it seems that they would strip copper and maybe lead engine parts at an excessive rate...maybe over time it could amount to dimensional changes in engine parts. Kind of like pouring bleach into your crankcase! I continued my tests last night too. I whiped the penny that was tested last night with a paper towel to see if the oxide layer would now come off but it did not. The penny got slightly more shiny but it was still same dark color and paper towel didn't seem to show any copper oxides on it. So I then put the penny back in the cup and continued heating it for another 1.5 hours with no change. I then decided that things were not going to change in the amount of time I'm willing to test it so I tried something strange. I put a blob of Zymol car wax in the oil cup containing the penny and hot oil. I know the Zymol will strip a penny if you rub it on it with a paper towel and I wanted to see if the Zymol could mix with the oil and clean the penny without agitation. Result: the Zymol would not mix with the hot oil so I just moved the blob of Zymol over the penny and let it cook for 30 minutes. Finally a change! The penny was "splotchy" now. Parts of it were stripped but not all of it. I guess the parts of the blog in direct contact with the penny were able to strip the penny but the parts not contacted weren't changed. This proves that agitation/circulation is not needed to strip the penny if the chemicals used are right for the job. I was worried that my earlier tests were invalid because the oil was stagnant but this latter finding eases that concern. My conclusion: Castrol Syntec 5W-40 cannot strip copper oxide coatings in a few hours. The only chance it has for being able to remove such coatings is to be given a really long time which I'm not willing to test! So far, your results with Redline and Havoline seem at most only slightly different than mine (you saw a green color that I didn't see but penny still was brown). I've heated Redline and it never turned green so I think the green you saw was indeed from cleaning the copper somewhat. Your tests differed from mine in length of test and my penny was completeley submerged in oil while your had drops of oil but I doubt the latter matters much. Well it looks like you got some more tests to do while all hope is lost for my Syntec 5W-40 to perform these miracle cleanings! Thanks for your results. Among other things, you saved me from having to buy Redline just for testing.
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