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#1146784 - 05/08/08 11:54 AM Oil Shear and Oil Thickening
Oil Changer Offline


Registered: 08/28/06
Posts: 1413
Loc: Detroit Metro
If I understand correctly, 10W-30 is a 10wt oil w/ VII added so it acts like a 30wt at temp. So oil shear is when the oil breaks down and does not act like a 30wt. at temp? What causes oil shear?

I also read here that oil thickens when it is too old(?). What causes oil to thicken? Is it possible for oil to shear AND thicken at the same time, or does it shear then thicken???

Help a guy out, will ya?

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#1146799 - 05/08/08 12:21 PM Re: Oil Shear and Oil Thickening [Re: Oil Changer]
ericthepig Offline


Registered: 12/26/06
Posts: 1648
Loc: Little Rock, AR
For shearing - read this -

http://www.bobistheoilguy.com/oilshear.htm

I believe thickening is caused when the smaller lighter molecules in an oil evaporate out over time and leave heavier molecules behind - thus a thickening affect.

(edit - for those that don't want to read the above article - the VII (viscosity index improvers) are long molecules - they literally get chopped up (sheared) mechanically in the engine over time).


Edited by ericthepig (05/08/08 12:24 PM)
_________________________
'06 Mazda 6 (97k) - Pennz YB 5w20 for summer (1 filter/yr)
'98 Sienna - (87k) - Pennz YB 5w30 1 yr OCI (but only ~5k miles)

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#1146807 - 05/08/08 12:29 PM Re: Oil Shear and Oil Thickening [Re: ericthepig]
ericthepig Offline


Registered: 12/26/06
Posts: 1648
Loc: Little Rock, AR
The article also answers another part of your question -

"After a period of time shearing, the oil will lose it's ability to hold up to the same flow as before since the VI Improvers are breaking down causing the oil to thin down in grade. Once this happens, there is less film strength between the mating surfaces so it doesn't take as much for the oil to shear, therefore creating more heat which attacks the base oil even more and then starts to cause the oil to thicken up due to the excessive levels of heat and the broken down VI Improvers become a contaminant which added to the existing oil will continue to thicken and ultimately cause sludge if not changed in a reasonable time."

So yes, oil shear initially causes thinning, but then can ultimately cause thickening.


Edited by ericthepig (05/08/08 12:30 PM)
_________________________
'06 Mazda 6 (97k) - Pennz YB 5w20 for summer (1 filter/yr)
'98 Sienna - (87k) - Pennz YB 5w30 1 yr OCI (but only ~5k miles)

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#1146808 - 05/08/08 12:29 PM Re: Oil Shear and Oil Thickening [Re: ericthepig]
Harley Anderson Offline


Registered: 08/03/06
Posts: 392
Loc: State College, PA
OIL VISCOSITY
The viscosity of oils are a most important quality, a key factor in oil performance. If the oil thins out, bearing surfaces will touch (collapse), resulting in metal-to-metal contact. This causes catastrophic bearing wear. Without the lubricant to act as a cushion, bearings and camshafts will gall. Cylinder walls also are subjected to high forces, and will suffer from piston and ring wear.
Viscosity is the thickness or "weight" (w) of an oil. It is represented as a number such as "10w-30." Polymeric thickeners (AKA viscosity improvers or VI's) are added so the oil will thicken as it gets hotter. A typical 5w-30 petroleum oil is made of 5-weight base oil. At zero degrees Celsius (32 degrees F.) it behaves like 5-weight oil. Because of VIís, it will behave like a 30-weight oil at 100 degrees C. (212 degrees F.)

Some places in the piston have a normal operating temperature of at least 600 degrees, and turbochargers get even hotter than that. This causes thermal degradation. The problem occurs during high RPM and temperatures. Oils "shear back" to the lower number--just when it is needed to be thicker. A 5-30 turns into a 5-weight oil.

Petroleum-based lubricants contain very large molecules, and especially suffer from thermal degradation when exposed to high engine temperatures. When this happens, they also form varnish deposits, which stick rings to the pistons and plug up turbo oil passages. Once a petroleum based oil reaches 475 degrees, it breaks down, turns into tar and varnish and then forms hard deposits that block the oil flow.

Petroleum oils also lose considerable viscosity at high engine temperatures and RPM. When petroleum oil enters an area of high stress and heavy loading, such as a bearing, the large molecules align themselves creating a path of least resistance. The rest of the petroleum oil follows this path, instead of coating the entire surface. The oil viscosity quickly drops, and the oil begins shearing back to the base number.

Contaminates such as dirt, moisture and sludge will also lower an oilís capability to maintain viscosity.

DETERGENTS
To prevent sludge formation, a detergent-dispersant additive is used in engine oil. This additive is usually a high--molecular weight nitrogen compound.
When sludge precursors begin to accumulate in the engine, mainly by-products of combustion blowby , the nitrogen encircles the by-products, keeping them from interacting and in suspension until the oil is changed. If they combine, they'll form long chains of molecules that become sludge deposits.

However, heat and thermal cycling depletes the detergents, then the sludge will begin to coat the inside of the engine, plug oil passages and cause catastrophic engine damage. This is an important consideration any time you extend oil drain intervals over recommended time or mileage.

ACID NEUTRALIZERS
As the engine operates, combustion gasses acidic by-products from the sulfur in the fuel. The acids combine with moisture (every gallon of gasoline burnt produces Ĺ gallon of moisture) which dissolve bearing surfaces.
All modern motor oils contain sodium hydroxides (NaOH) to combat the acid build up in the oil. As the oil becomes contaminated and turns acid, the NaOH gets used up. Preventing acid buildup is one of the primary reasons for changing motor oil. Short trip driving is the worst kind of driving for this problem as moisture is not boiled off during driving cycles.

Because everyone's driving habits are different, everyone's oil gets contaminated at a different rate. And since various oils contain different amounts of NaOH, the only real way to tell if your oil is acid contaminated is by having it analyzed.

The TBN* represents the number of grams of NaOH per kilogram of oil. New oil comes with a TBN number ranging from 5 to 12, depending on the quality of the oil. Store bought oils have a TBN of 6. High quality synthetics have a TBN of as high as 12. When the TBN drops below 2, itís time to change it.

Taken from here:
http://www.waynesgarage.com/docs/oil.htm
_________________________
2005 Dodge Ram 2500, CTD, NV5600, Frantz BP Filter, Baldwin Coolant Filter, Amsoiled.

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#1146842 - 05/08/08 01:21 PM Re: Oil Shear and Oil Thickening [Re: Harley Anderson]
Pablo Offline


Registered: 10/28/02
Posts: 46692
Loc: Duvall WA - Pacific NW USA
 Quote:
are added so the oil will thicken as it gets hotter


-10 points.

TNTC.

F

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#1146845 - 05/08/08 01:26 PM Re: Oil Shear and Oil Thickening [Re: Pablo]
Nickdfresh Offline


Registered: 03/15/06
Posts: 3487
Loc: Buffalo, NY
 Originally Posted By: Pablo
 Quote:
are added so the oil will thicken as it gets hotter


-10 points.

TNTC.

F



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#1146846 - 05/08/08 01:31 PM Re: Oil Shear and Oil Thickening [Re: Nickdfresh]
DmanWho Offline


Registered: 07/26/07
Posts: 578
Loc: Oregon
I believe oxidation may cause oil thickening.

I might be the only one here that thinks so... It's "sound science" I tell ya!

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#1146898 - 05/08/08 02:57 PM Re: Oil Shear and Oil Thickening [Re: Pablo]
Oil Changer Offline


Registered: 08/28/06
Posts: 1413
Loc: Detroit Metro
 Originally Posted By: Pablo
 Quote:
are added so the oil will thicken as it gets hotter


-10 points.

TNTC.

F


What is "TNTC"? These "polymeric thickeners" - is that what BITOG clan usually refer to as "long-chain polymers"? Do these VII's get longer when hot and shorter when cool, or vice-versa? If saying "causes the oil to get thicker when hot", what is the best way to explain their function?
What is "TNTC"? The

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#1146899 - 05/08/08 02:58 PM Re: Oil Shear and Oil Thickening [Re: Oil Changer]
Oil Changer Offline


Registered: 08/28/06
Posts: 1413
Loc: Detroit Metro
Thanks for the great and quick responses, guys. I'm going to read the links right now.

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#1146902 - 05/08/08 03:00 PM Re: Oil Shear and Oil Thickening [Re: Oil Changer]
Pablo Offline


Registered: 10/28/02
Posts: 46692
Loc: Duvall WA - Pacific NW USA
TNTC = too numerous to count....as in too many errors in that paper, so I gave it a big fat F

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#1146904 - 05/08/08 03:01 PM Re: Oil Shear and Oil Thickening [Re: Oil Changer]
Pablo Offline


Registered: 10/28/02
Posts: 46692
Loc: Duvall WA - Pacific NW USA
 Originally Posted By: Oil Changer
Thanks for the great and quick responses, guys. I'm going to read the links right now.


careful - that "waynesgarage" piece is full of [censored]

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#1146906 - 05/08/08 03:05 PM Re: Oil Shear and Oil Thickening [Re: Harley Anderson]
Pablo Offline


Registered: 10/28/02
Posts: 46692
Loc: Duvall WA - Pacific NW USA
 Quote:
All modern motor oils contain sodium hydroxides (NaOH)


Seriously wrong information. Warning.

Some people who just don't know what they are writing about should not be allowed to be alone on the net!

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#1146907 - 05/08/08 03:06 PM Re: Oil Shear and Oil Thickening [Re: Pablo]
Harley Anderson Offline


Registered: 08/03/06
Posts: 392
Loc: State College, PA
sorry pabs, first thing that came up on a google search. I figured a so called expert could explain things better than me.
_________________________
2005 Dodge Ram 2500, CTD, NV5600, Frantz BP Filter, Baldwin Coolant Filter, Amsoiled.

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#1146908 - 05/08/08 03:08 PM Re: Oil Shear and Oil Thickening [Re: Harley Anderson]
Pablo Offline


Registered: 10/28/02
Posts: 46692
Loc: Duvall WA - Pacific NW USA
 Originally Posted By: Harley Anderson
sorry pabs, first thing that came up on a google search. I figured a so called expert could explain things better than me.


Not your fault - why the heck did that guy think he is an expert in the first place?

It's from "Provided by Nutz & Boltz Newsletter" ....

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#1146911 - 05/08/08 03:14 PM Re: Oil Shear and Oil Thickening [Re: Oil Changer]
Happy Birthday Tempest Offline


Registered: 03/21/06
Posts: 10468
Loc: Las Vegas NV
 Quote:
Do these VII's get longer when hot and shorter when cool, or vice-versa? If saying "causes the oil to get thicker when hot", what is the best way to explain their function?

They expand and contract when hot/cold. They are statistical coils and not really a spring type helix. And they "plump up" the viscosity of oils at higher temps that would otherwise be too thin at those temps. When these very large molecules get sheared (mechanically broken) they loose their vis boosting ability and the oils thin at higher temps. Not all VII is the same, some are better at resisting this.
_________________________
ďNever underestimate the difficulty of changing false beliefs by facts.Ē --- Henry Rosovsky

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