3:1 silicon:aluminum in UOAs for sand

[paulri]

I was reading here (http://www.machinerylubrication.com/Read/1356/silicon-oil-source) that when sand is present in oil, there will be a silicon:aluminum ratio of 3:1.

This seemed at first glance to be very helpful, when looking at a UOA, to see if the problem was sand. But the article itself cautioned that there are plenty of other sources of silicon, and of course aluminum parts could provide that into the oil.

So is this ratio true (for sand)?

And is it helpful in trying to determine if sand caused high wear metal rates?

 

[Kestas]

Sand is chiefly silicon oxide with some aluminum in it. My experience shows the ratio is less than 3:1, having less silicon.

 

[Ihatetochangeoil]

I enjoy reading at Machinery Lubrication and have been running UOA since long before I joined BITOG, but I don't see their correlation holding true in my experience. I most certainly agree that most test labs caution Si ppm above 20; and Mr. Alan Bender (Lab Director at Polaris) has informed me via phone conversation that "Iron and Silicon are the two worst things you can have in your oil." Iron is literally your engine disintegrating (microscopically); and silicon is rock, harder than iron.

Generally, silicon is ingested through your air intake; and not only are there many aftermarket air filters, there are many knowledgeable mechanics who claim that your air filter is the most important filter on your engine. You can do some reading over at Blackstone Labs and they will tell you that there are sources of silicon in your oil other than atmospheric contamination (such as gasket sealer curing from a [recent?] repair), and some antifreezes contain Silicon...It helps to have several UOA reports so that trends can be established.

It also helps to have a virgin oil analysis, because some motor oils have small amounts of Si in their blends as new. I'm running Amsoil 5W30 Full Synthetic, and my new oil has 6 ppm Si.

If you Wikipedia Silicon, it agrees with what Machinery Lubrication has to say.
https://en.wikipedia.org/wiki/Silicon

Silicon is the eighth most common element in the universe by mass, but very rarely occurs as the pure free element in the Earth's crust. It is most widely distributed in dusts, sands, planetoids, and planets as various forms of silicon dioxide (silica) or silicates. Over 90% of the Earth's crust is composed of silicate minerals, making silicon the second most abundant element in the Earth's crust (about 28% by mass) after oxygen.

I don't think I've ever seen a Used Oil Analysis without some silicon in it, but the less the better. And I have nothing but logic, but it stands to reason that if Silicon is high in your oil, it would most certainly could have an (abrasive) effect on other metals.

Thanks for posting the article from machinery lubrication, I enjoy reading such. The more sources of information one has, generally the better, and the better chance one has of knowing B*** when one sees it.

 

[paulri]

Originally Posted By: Ihatetochangeoil
I enjoy reading at Machinery Lubrication and have been running UOA since long before I joined BITOG, but I don't see their correlation holding true in my experience.


Just so that I understand what your point is--you are saying that you don't believe that sand in oil will show up in a UOA with a 3:1 si:al ratio--or that it always does?

 

[MolaKule]

Silicon isn't necessarily sourced from sand.

Silicon can leach from silicone-based RTV gasket materials as well.

In many cases the 1 ppm of iron and or aluminum found in VOA's are from additives.

So bottom line is, there is no rule of thumb ratio.

 

[weasley]

Not to forget the silicon in a VOA coming from antifoam, which can be added to the finished oil and/or to the additives within it. It is usually fairly low, but is almost always there.

 

[paulri]

OK, if silicon from sand will be present in oil in a 3:1 ratio of si:al, then we could rule out sand as the culprit, if silicon is present in a UOA, but there is not a corresponding increase in aluminum, correct?

I do realize that there are other sources of silicon in oil. The article linked to in the OP stated this. I don’t see that as the relevant issue here, however. If there is a spike in silicon, but aluminum is flat, then that would rule out sand, would it not?

 

[SuperSalad]

The guideline is meant as just that. It is not absolute and it lists it's own limited usefulness in an unknown situation.

I have found this useful over the years when I've seen silicone show up, but not the corresponding amount of aluminum indicating it is likely not dirt. Alternatively I've gotten pretty much that spot on ratio, to tell me that it is definitely dirt. As always, you cannot simply look at a single number and make a determination based on it, but it is yet another marker that can point you to the correct conclusion.

It is especially useful in a machine without aluminum parts and non-silicone seals.

 

[SuperSalad]

Originally Posted By: paulri
OK, if silicon from sand will be present in oil in a 3:1 ratio of si:al, then we could rule out sand as the culprit, if silicon is present in a UOA, but there is not a corresponding increase in aluminum, correct?

I do realize that there are other sources of silicon in oil. The article linked to in the OP stated this. I don’t see that as the relevant issue here, however. If there is a spike in silicon, but aluminum is flat, then that would rule out sand, would it not?

And yes, if you have one present but not the other, your investigation should likely be pointing you to a different conclusion.

If the dirt contamination is high enough, sodium should start showing up too since it is one of the more abundant elements of "dirt". Although it too could have other sources.

 

[paulri]

Originally Posted By: MotoTribologist
And yes, if you have one present but not the other, your investigation should likely be pointing you to a different conclusion.

If the dirt contamination is high enough, sodium should start showing up too since it is one of the more abundant elements of "dirt". Although it too could have other sources.


Fair enough.

I just wanted to make sure that I was understanding this correctly. Oil and cars are not my background, so it never hurts to double check.

 

[m37charlie]

Silica in the form of sand is a weathering product of silicate rocks in the Earth's crust. These primarily include for example granite and basalt. The silicates are primarily aluminum iron potassium and magnesium in the source rocks. The weathering of silicates involves a conversion to carbonates which are carried to the ocean and buried on the continental shelf or deep ocean plains. This incidentally is a proposed mechanism for how tectonic activity reduces carbon dioxide levels on a long term basis. At any rate the above for metals are going to be present mixed with sand in variable percentages that depend completely on the source rocks.
The theory of carbon dioxide drawdown caused by mountain uplift is the reason people think they're earth started cooling down and ice started on Antarctica about 30 million years ago right about when India ran into Eurasia and caused the uplift of the Tibetan plateau.
Charlie