Taking an oil sample from a cold engine

[See6Z06]

Hey everyone,

I recently took an oil sample from my Corvette C6 Z06 after the car had been sitting cold for a couple of weeks. I sent this sample to ALS labs via NAPA and it came back with surprisingly low metal levels in the oil.

I know the correct procedure for getting the most accurate oil analysis is to take the sample after the engine has been run up to temperature so I am wondering whether taking an oil sample after the engine has been sitting a while, will present more or less metal in the oil?

I know that a cold oil sample wont show anything useful in terms of water or fuel dilution, I am choosing to focus on metal levels for this discussion. In my mind, taking a cold oil sample should present a worse case scenario in terms of metal levels due to the metal having settled at the bottom of the oil pan after sitting for a long time. Is that thought accurate? Or rather, would warm oil have more metal suspended in it and therefore show a higher metal reading?

For context, the last two oil changes have shown the oil to be somewhat glittery, but the engine shows no loss in oil pressure or any signs of distress and that first oil analysis i sent out showed lower than average metal in the oil compared to other LS7 reports that I have seen. Therefore, I am trying to get an accurate idea of what metal is actually in the oil and how much there is.

Thanks everyone.

 

[kschachn]

A lot going on there. Just be aware that unless special processing takes place on the sample, any metal you can see (or would settle out) will not be reflected in the spectrographic analysis. If you have glittery oil then there is something seriously wrong and I'd be more worried about that than the temperature of my sample.

 

[Al]

It really doesn't matter in my opinion. Addition moisture will not get into the oil. You always want to get the oil from the middle of the crankcase to avoid the heavy metals. Just an opinion. You would have to do tests on it

 

[See6Z06]

A lot going on there. Just be aware that unless special processing takes place on the sample, any metal you can see (or would settle out) will not be reflected in the spectrographic analysis. If you have glittery oil then there is something seriously wrong and I'd be more worried about that than the temperature of my sample.

Well, I am worried about it but i can't really troubleshoot the cause unless I know what metal it is, thus the oil analysis. The only other way to diagnose is to tear apart the whole engine, which isn't practical or necessary given the lack of any performance or oil pressure depreciation.

 

[kschachn]

Well, I am worried about it but i can't really troubleshoot the cause unless I know what metal it is, thus the oil analysis. The only other way to diagnose is to tear apart the whole engine, which isn't practical or necessary given the lack of any performance or oil pressure depreciation.

You need an acid digestion of the sample or SEM/EDX on the particles.

Can you post those prior normal UOA?

 

[See6Z06]

You need an acid digestion of the sample or SEM/EDX on the particles.

Can you post those prior normal UOA?

Here you go!

 

[kschachn]

If that were my expensive car and engine, and I had glittery oil I would definitely try and find out what the glitter is.

Just an aside what is being caught in the filter?

 

[See6Z06]

If that were my expensive car and engine, and I had glittery oil I would definitely try and find out what the glitter is.

Just an aside what is being caught in the filter?

Can I ask ALS to do the analysis that you suggest on another sample i send them?

Because outside of an oil analysis, i dont see how i can find out where the glitter came from without tearing the whole motor apart.

 

[kschachn]

It says they do wear particle analysis and it appears this includes ferrography as well as EDX. I’m sure it isn’t cheap but you’ll get an answer.

 

[SubieRubyRoo]

The best way to determine what it meant would have been to take that completely cold sample, then have started up before draining the oil, gotten it up to temp and taken another sample of the same oil.

TestOil in OH also does ferrography, and the pricing isn't incredibly expensive considering the real value of data you get from that analysis.

 

[See6Z06]

The best way to determine what it meant would have been to take that completely cold sample, then have started up before draining the oil, gotten it up to temp and taken another sample of the same oil.

TestOil in OH also does ferrography, and the pricing isn't incredibly expensive considering the real value of data you get from that analysis.

I guess i dont understand how spectrographic analysis wouldnt pick up any of the metal in the oil. I think that if there is enough metal for me to see it in the oil, it must leave enough trace amounts of it in the oil for spectrography to pick up. It's not like any of the metal in the oil was large enough for me to pick up and there wasnt even much, if any, left on the drain pan.

 

[kschachn]

I guess i dont understand how spectrographic analysis wouldnt pick up any of the metal in the oil. I think that if there is enough metal for me to see it in the oil, it must leave enough trace amounts of it in the oil for spectrography to pick up. It's not like any of the metal in the oil was large enough for me to pick up and there wasnt even much, if any, left on the drain pan.

Sometimes but not always. When I ran oil analysis in college for our fluid power and automotive engineering departments you could have samples that showed nothing abnormal until an acid digestion was done. ICP (and back then AA) measure elements in solution, not particles. Particles are filtered out because they destabilize the plasma and the analysis. It’s not the tool to measure particles. Anything you can see is too large.

If you have visible metal in an engine oil sample you’re not seeing wear, you’re seeing failure.

 

[RDMgr]

ICP will analyze particles suspended in oil. The problem with ICP is it will only see particles up to 5-7 microns. Larger particles can cause aspiration plugging and some may be too large to aspirate. This is the reason for running other detection methods such as EDXRF, PQ or rotrode filter. ICP and PQ are routine methods. EDXRF and RFS are probably considered exception methods in most commercial labs that run the methods

Ferrography is an excellent tool for looking at particle morphology and possibly particle sources. Short of being able to perform ferrography, a patch test may give you the visual you need.

You really only get a true wear metal profile and a meaningful particle size distribution by taking a hot sample and using these tools.

 

[kschachn]

ICP will analyze particles suspended in oil. The problem with ICP is it will only see particles up to 5-7 microns. Larger particles can cause aspiration plugging and some may be too large to aspirate. This is the reason for running other detection methods such as EDXRF, PQ or rotrode filter. ICP and PQ are routine methods. EDXRF and RFS are probably considered exception methods in most commercial labs that run the methods

Ferrography is an excellent tool for looking at particle morphology and possibly particle sources. Short of being able to perform ferrography, a patch test may give you the visual you need.

You really only get a true wear metal profile and a meaningful particle size distribution by taking a hot sample and using these tools.

Even then it’s not a given based on the aerodynamic diameter, sometimes the “particle size” it will see is much smaller.

 

[RDMgr]

Even then it’s not a given based on the aerodynamic diameter, sometimes the “particle size” it will see is much smaller.

If a particle is small enough to be aspirated into the plasma, particle size is irrelevant. The ICP doesn’t analyze the particle. Once the particle enters the plasma it is vaporized regardless of its size. Once vaporized, the various elemental components of the various particles and the carrier fluid try to achieve the ground state. In doing this each element emits light of a specific wavelength which is detected and measured. The measured emissions relate back to a concentration and reported, typically in ppm. The same is true for RDE and RFS.

 

[kschachn]

If a particle is small enough to be aspirated into the plasma, particle size is irrelevant. The ICP doesn’t analyze the particle. Once the particle enters the plasma it is vaporized regardless of its size. Once vaporized, the various elemental components of the various particles and the carrier fluid try to achieve the ground state. In doing this each element emits light of a specific wavelength which is detected and measured. The measured emissions relate back to a concentration and reported, typically in ppm. The same is true for RDE and RFS.

Yeah I know how a spectrographic analysis works. But it also has to do with the density of the specific particles. I disagreed mostly with the idea that a 7 micron particle will be analyzed.

 

[Sonny88]

So in 2000 miles, the TBN is down to 2.6

 

[RDMgr]

Yeah I know how a spectrographic analysis works. But it also has to do with the density of the specific particles. I disagreed mostly with the idea that a 7 micron particle will be analyzed.

Particles are not analyzed. Particles are vaporized and their emissions are analyzed and related to a concentration. Once the particle is vaporized there is no particle. If you want to specifically analyze a 7-micron particle or any particle for that matter, you can destroy it. The particle must remain intact and a nondestructive method used to analyze it.