Fuel dilution and shearing

[Danh]

There's been a lot of discussion about fuel dilution here, particularly in direct injection engines, and a seeming consensus and belief that this is what causes a reduction in used oil viscosity.

As a recent recipient of quickly and badly sheared oil in a DI used oil analysis, this was my first assumption. But I think it's mostly wrong.

For example, assume an engine that holds 5 quarts (160 oz) of oil had 5% (really a lot - 8 oz) of fuel dilution. Gasoline has a 100C cSt of between .4 and .7. Assuming the crankcase was filled with an xx-20 oil with a new cSt of 8.7 and we use the low end of the gasoline cSt, the combined mixture would look like:

Oil 160 oz * 8.7 = 1392.0
Fuel 8oz * .4 = 3.2
Total 168 oz. 1395.2

1395.2/168 = 8.3= cSt of combined

Unless something else chemical goes on here, it seems an almost worst-case scenario would reduce this oil's cSt by only .4. And a more typical fuel dilution of 1-2% would only reduce cSt by .1-.15. So, when we see cSt reductions in a used oil analysis from say 8.7 to 7.0 with 1-2% fuel dilution, fuel accounts for only a small part of the shearing. Barring coolant contamination, the rest must therefore be caused by mechanical forces. So comments like "..that fuel dilution really beat up the viscosity...", don't seem quite right.

Does this make sense to others?

 

[double vanos]

Never thought about it like you're doing, but an excellent line of thought.. Good read! Thanks!

 

[d00df00d]

Originally Posted By: Danh
Barring coolant contamination, the rest must therefore be caused by mechanical forces.

Or chemical reaction. I feel like I've heard something about fuel beating up VIIs. Can anyone more informed confirm or deny?

 

[OneEyeJack]

Could the UOA numbers be that of a static sample that has had some time to cook off a bit without the ongoing process to continue to contribute to the contamination and be less than the actual number when the engine is hot and running?

 

[TheOnlySarge]

Hey Danh....it is what fuel does to the add packs of the oil. Dilutes and renders them less than efficient to do their job.
Small amounts of fuel left in the engine oil from say...short trips etc. that do not allow the engine to come up to temp to burn off the fuel in the sump cause significant degradation to the lubrication qualities of oil.

 

[Danh]

Originally Posted By: TheOnlySarge
Hey Danh....it is what fuel does to the add packs of the oil. Dilutes and renders them less than efficient to do their job.
Small amounts of fuel left in the engine oil from say...short trips etc. that do not allow the engine to come up to temp to burn off the fuel in the sump cause significant degradation to the lubrication qualities of oil.


Yeah, I get fuel dilution is bad for a number of reasons; probably the least significant of which is its effect on viscosity. I was just questioning whether the frequent comment here that viscosity was down because of fuel dilution may not be quite right.

 

[Shannow]

I've posted same thing a while ago trying to ascertain how a kerosene flush and fuel dilution were linked, and as you found, it doesn't work.

Here's a discussion on what fuel does (well is conjectured to do) to VIIs

https://bobistheoilguy.com/forums/ubbthreads.php/topics/893022/Double-Super-Secret_5W-40_Audi

 

[TheOnlySarge]

Originally Posted By: Danh
Originally Posted By: TheOnlySarge
Hey Danh....it is what fuel does to the add packs of the oil. Dilutes and renders them less than efficient to do their job.
Small amounts of fuel left in the engine oil from say...short trips etc. that do not allow the engine to come up to temp to burn off the fuel in the sump cause significant degradation to the lubrication qualities of oil.


Yeah, I get fuel dilution is bad for a number of reasons; probably the least significant of which is its effect on viscosity. I was just questioning whether the frequent comment here that viscosity was down because of fuel dilution may not be quite right.

Well sir I believe what the labs dont say is the viscosity is down due fuel in the oil ....but......that it is caused not by VII dilution but the fuel minimizing and degrading the add packs that maintain a healthy oil viscosity.

 

[Danh]

Originally Posted By: Shannow
I've posted same thing a while ago trying to ascertain how a kerosene flush and fuel dilution were linked, and as you found, it doesn't work.

Here's a discussion on what fuel does (well is conjectured to do) to VIIs

https://bobistheoilguy.com/forums/ubbthreads.php/topics/893022/Double-Super-Secret_5W-40_Audi



Gosh, a 27 page thread. I gather the gist of this is that the viscosity degradation may result from fuel's influence on VIIs, i.e. a chemical reaction? If this is the case, the fewer VIIs, the more likely a fuel-diluted oil is to stay in grade?

And, as I reach escape velocity from my knowledge base, if PAO-based oils require fewer VIIs, a Mobil 1 Extended Performance 0w20 with c.70% PAO would fare better than Mobil 1 Advanced Fuel Economy with c.35% in handling fuel dilution?

 

[Danh]

Originally Posted By: TheOnlySarge
Originally Posted By: Danh
Originally Posted By: TheOnlySarge
Hey Danh....it is what fuel does to the add packs of the oil. Dilutes and renders them less than efficient to do their job.
Small amounts of fuel left in the engine oil from say...short trips etc. that do not allow the engine to come up to temp to burn off the fuel in the sump cause significant degradation to the lubrication qualities of oil.


Yeah, I get fuel dilution is bad for a number of reasons; probably the least significant of which is its effect on viscosity. I was just questioning whether the frequent comment here that viscosity was down because of fuel dilution may not be quite right.

Well sir I believe what the labs dont say is the viscosity is down due fuel in the oil ....but......that it is caused not by VII dilution but the fuel minimizing and degrading the add packs that maintain a healthy oil viscosity.


So a chemical reaction, like Shannow is also pointing out. Interesting.

 

[DWC28]

Originally Posted By: Danh
There's been a lot of discussion about fuel dilution here, particularly in direct injection engines, and a seeming consensus and belief that this is what causes a reduction in used oil viscosity.

As a recent recipient of quickly and badly sheared oil in a DI used oil analysis, this was my first assumption. But I think it's mostly wrong.

For example, assume an engine that holds 5 quarts (160 oz) of oil had 5% (really a lot - 8 oz) of fuel dilution. Gasoline has a 100C cSt of between .4 and .7. Assuming the crankcase was filled with an xx-20 oil with a new cSt of 8.7 and we use the low end of the gasoline cSt, the combined mixture would look like:

Oil 160 oz * 8.7 = 1392.0
Fuel 8oz * .4 = 3.2
Total 168 oz. 1395.2

1395.2/168 = 8.3= cSt of combined

Unless something else chemical goes on here, it seems an almost worst-case scenario would reduce this oil's cSt by only .4. And a more typical fuel dilution of 1-2% would only reduce cSt by .1-.15. So, when we see cSt reductions in a used oil analysis from say 8.7 to 7.0 with 1-2% fuel dilution, fuel accounts for only a small part of the shearing. Barring coolant contamination, the rest must therefore be caused by mechanical forces. So comments like "..that fuel dilution really beat up the viscosity...", don't seem quite right.

Does this make sense to others?


Viscosity calculation is not linear. 95% 8.7 cSt @ 100 C plus 5 % 0.5 cSt @ 100C results in 100% of 6.52 cSt @ 100C

 

[Danh]

Originally Posted By: DWC28
Originally Posted By: Danh
There's been a lot of discussion about fuel dilution here, particularly in direct injection engines, and a seeming consensus and belief that this is what causes a reduction in used oil viscosity.

As a recent recipient of quickly and badly sheared oil in a DI used oil analysis, this was my first assumption. But I think it's mostly wrong.

For example, assume an engine that holds 5 quarts (160 oz) of oil had 5% (really a lot - 8 oz) of fuel dilution. Gasoline has a 100C cSt of between .4 and .7. Assuming the crankcase was filled with an xx-20 oil with a new cSt of 8.7 and we use the low end of the gasoline cSt, the combined mixture would look like:

Oil 160 oz * 8.7 = 1392.0
Fuel 8oz * .4 = 3.2
Total 168 oz. 1395.2

1395.2/168 = 8.3= cSt of combined

Unless something else chemical goes on here, it seems an almost worst-case scenario would reduce this oil's cSt by only .4. And a more typical fuel dilution of 1-2% would only reduce cSt by .1-.15. So, when we see cSt reductions in a used oil analysis from say 8.7 to 7.0 with 1-2% fuel dilution, fuel accounts for only a small part of the shearing. Barring coolant contamination, the rest must therefore be caused by mechanical forces. So comments like "..that fuel dilution really beat up the viscosity...", don't seem quite right.

Does this make sense to others?


Viscosity calculation is not linear. 95% 8.7 cSt @ 100 C plus 5 % 0.5 cSt @ 100C results in 100% of 6.52 cSt @ 100C


Learn new things every day, and this would explain it. Where does this calculation come from?

 

[Danh]

Originally Posted By: DWC28
Originally Posted By: Danh
There's been a lot of discussion about fuel dilution here, particularly in direct injection engines, and a seeming consensus and belief that this is what causes a reduction in used oil viscosity.

As a recent recipient of quickly and badly sheared oil in a DI used oil analysis, this was my first assumption. But I think it's mostly wrong.

For example, assume an engine that holds 5 quarts (160 oz) of oil had 5% (really a lot - 8 oz) of fuel dilution. Gasoline has a 100C cSt of between .4 and .7. Assuming the crankcase was filled with an xx-20 oil with a new cSt of 8.7 and we use the low end of the gasoline cSt, the combined mixture would look like:

Oil 160 oz * 8.7 = 1392.0
Fuel 8oz * .4 = 3.2
Total 168 oz. 1395.2

1395.2/168 = 8.3= cSt of combined

Unless something else chemical goes on here, it seems an almost worst-case scenario would reduce this oil's cSt by only .4. And a more typical fuel dilution of 1-2% would only reduce cSt by .1-.15. So, when we see cSt reductions in a used oil analysis from say 8.7 to 7.0 with 1-2% fuel dilution, fuel accounts for only a small part of the shearing. Barring coolant contamination, the rest must therefore be caused by mechanical forces. So comments like "..that fuel dilution really beat up the viscosity...", don't seem quite right.

Does this make sense to others?


Viscosity calculation is not linear. 95% 8.7 cSt @ 100 C plus 5 % 0.5 cSt @ 100C results in 100% of 6.52 cSt @ 100C


Thanks. Your post inspired me to look for the Widman calculator. Putting these numbers in gave me a 100C cSt of 7.52. And a 1% fuel dilution 8.45. Any idea why they differ?

 

[zeng]

Would love to read more on the formula/assumptions used in calculating viscosity post blending ..

 

[Shannow]

Danh,
I knew that I'd seen something in my travels on actual measurements of what you are attempting.

Have fun

http://hrcak.srce.hr/file/75680

 

[Danh]

Originally Posted By: zeng
Would love to read more on the formula/assumptions used in calculating viscosity post blending ..

Try this:

www.Widman.Biz/English/Calculators/Mixtures.html

 

[DWC28]

Thanks. Your post inspired me to look for the Widman calculator. Putting these numbers in gave me a 100C cSt of 7.52. And a 1% fuel dilution 8.45. Any idea why they differ? [/quote]

My calculator is home grown. This extreme case of viscosity blending may be outside of it's capability as I don't usually blend with a component as low as 0.5 cSt.