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Reading back through an older thread that @Gokhan posted today, with his more complex viscosity calculator (the caveat being you need to know alpha for it to be accurate) with the idea of it being more useful for mixing dissimilar fluids I recalled some recent discussions about the impact of gasoline on viscosity.
Thread can be found here:
Now, I'm going to preface this with a couple of caveats:
1. There's always some error in measured viscosity
2. PDS viscosity also varies slightly from measured, due to batch variation and #1
3. Used oil will be contaminated with more than just fuel, this will impact viscosity
4. Mechanical shear does happen, and we don't know how much
@Artem recently posted a thread with reports from two different labs:
1. Blackstone - Who does not directly measure fuel dilution using GC, rather, they infer it from FlashPoint, and don't compare measured flashpoint with virgin
2. Oil Analyzers - Who uses GC (Gas Chromatography) to directly measure fuel content
Thread here:
As expected, the fuel dilution figure inferred by Blackstone (
In that thread, I plugged in:
1. viscosity of gasoline: ~0.5cSt
2. the KV100 of the virgin oil in question: 10.8cSt
to the Widman visc calculator, which yielded a figure of 9.2cSt
This of course does not provide for the caveats noted above nor the fact that visc calcs used on dissimilar fluids, as @Gokhan pointed out, are inaccurate.
This is where we could have a bit of fun with Gokhan's calculator:
We have everything but the alpha figure available to us, including the densities of both fluids:
Havoline Pro-DS 5w-30:
KV100: 10.8cSt
Density: 0.8479
Gasoline:
KV100: 0.5cSt
Density: 0.75
If we work this backwards, we can get the UOA viscosity figure using an alpha of 1.55:
But what about the caveats? Exactly. We are just taking a stab at alpha here to make the KV100 match the measured figure; we are guessing. However, we could find alpha for this combo by having a sample of the virgin oil diluted with 4.8% fuel and tested, then adjusting alpha to match that figure.
This would give us the ability to determine, more accurately, the level of mechanical shear taking place in the presence of fuel dilution for a Group III-based synthetic oil. Based on the aforementioned discussion, the alpha figure changes by base oil type, so you'd need to re-determine it for different base oil and base oil blends, like PAO. I appreciate that this does hinder the utility of this exercise.
Let's say for the sake of example here, we determined, through actual testing, that alpha in this scenario was 1.2, so we apply that to our product:
Our KV100 should be 9.05cSt then, but we know it is 8.6cSt based on the UOA. So, our viscosity loss due to fuel is 1.75cSt (~16%), while through shear and other factors, 0.6cSt (~6%).
So, what is the ultimate utility here; what is the value of determining this if we already can get a firm figure on fuel content from a proper lab like OAI?
Well, if we were able to successfully find for alpha in this scenario, we'd have a much better understanding of the relationship between fuel and viscosity loss and potentially, why fuel may have a greater, or lesser, impact on viscosity than predicted. That would be valuable.
Thread can be found here:
Calculator for viscosity mixing based on the Lederer - Roegiers equation
I just realized that the Widman viscosity-mixing calculator and similar calculators on the Internet are totally useless. They are very inaccurate. After some brief reading, it looks like the Lederer - Roegiers equation works well. The only caveat is that there is an adjustable parameter alpha...
bobistheoilguy.com
Now, I'm going to preface this with a couple of caveats:
1. There's always some error in measured viscosity
2. PDS viscosity also varies slightly from measured, due to batch variation and #1
3. Used oil will be contaminated with more than just fuel, this will impact viscosity
4. Mechanical shear does happen, and we don't know how much
@Artem recently posted a thread with reports from two different labs:
1. Blackstone - Who does not directly measure fuel dilution using GC, rather, they infer it from FlashPoint, and don't compare measured flashpoint with virgin
2. Oil Analyzers - Who uses GC (Gas Chromatography) to directly measure fuel content
Thread here:
Havoline Pro-DS 5w30 -- 9,044 mi -- 2014 Mazda 3 with 2.0L
This is the third and final sample of this oil. I dragged this out until 15% oil life left and was just itching with anticipation to get under the car and change the oil and have a look around to make sure all is well. :sneaky: The 2nd sample @ 7,540 mile UOA thread can be found ——> HERE The...
bobistheoilguy.com
As expected, the fuel dilution figure inferred by Blackstone (
In that thread, I plugged in:
1. viscosity of gasoline: ~0.5cSt
2. the KV100 of the virgin oil in question: 10.8cSt
to the Widman visc calculator, which yielded a figure of 9.2cSt
This of course does not provide for the caveats noted above nor the fact that visc calcs used on dissimilar fluids, as @Gokhan pointed out, are inaccurate.
This is where we could have a bit of fun with Gokhan's calculator:
We have everything but the alpha figure available to us, including the densities of both fluids:
Havoline Pro-DS 5w-30:
KV100: 10.8cSt
Density: 0.8479
Gasoline:
KV100: 0.5cSt
Density: 0.75
If we work this backwards, we can get the UOA viscosity figure using an alpha of 1.55:
But what about the caveats? Exactly. We are just taking a stab at alpha here to make the KV100 match the measured figure; we are guessing. However, we could find alpha for this combo by having a sample of the virgin oil diluted with 4.8% fuel and tested, then adjusting alpha to match that figure.
This would give us the ability to determine, more accurately, the level of mechanical shear taking place in the presence of fuel dilution for a Group III-based synthetic oil. Based on the aforementioned discussion, the alpha figure changes by base oil type, so you'd need to re-determine it for different base oil and base oil blends, like PAO. I appreciate that this does hinder the utility of this exercise.
Let's say for the sake of example here, we determined, through actual testing, that alpha in this scenario was 1.2, so we apply that to our product:
Our KV100 should be 9.05cSt then, but we know it is 8.6cSt based on the UOA. So, our viscosity loss due to fuel is 1.75cSt (~16%), while through shear and other factors, 0.6cSt (~6%).
So, what is the ultimate utility here; what is the value of determining this if we already can get a firm figure on fuel content from a proper lab like OAI?
Well, if we were able to successfully find for alpha in this scenario, we'd have a much better understanding of the relationship between fuel and viscosity loss and potentially, why fuel may have a greater, or lesser, impact on viscosity than predicted. That would be valuable.
