UOAs: Thick oil and higher wear

[Ray Garlington]

Food for thought? Many have mentioned that on our UOA's thick oils show higher wear numbers. It is likely that this observation is correct; however, it does not necessarily follow that additional engine wear has occurred. The argument: We know that the wear metals we observe in UOAs have been suspended in the oil; however, other wear metal particles also went out the drain or were embedded in the oil filter. Therefore, what we may be observing is the thicker oil's ability to hold more wear particles in suspension. Is this possibly the case?

 

[csandste]

Interesting point.

 

[Al]

Food for thought-but I doubt it. The difference in viscosity is just not that huge. I guess one way to determine that would be to sample the same oil cold and hot and see if there is a difference. I must admit this a gut feeling on my part.

 

[MikeW]

I don't know why you think an higher viscosity oil would have a greater ability to hold particles in suspension. I've never heard a correlation between those two properties. More likely, the higher vis oil is less likely to reach the outer limits of the oiling system causing higher wear.

 

[Jay]

The wear metal particles that FTIR analysis measures are <5um. Particles <2um are colloidal and never settle out.

 

[MolaKule]

quote:

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We know that the wear metals we observe in UOAs have been suspended in the oil; however, other wear metal particles also went out the drain or were embedded in the oil filter. Therefore, what we may be observing is the thicker oil's ability to hold more wear particles in suspension. Is this possibly the case?

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Make that "wear metal molecules." The atoms or molecule elements due to wear are in solution in the oil, and represent very small particles too small to be caught by the filter material. These are the "sub-microscopic" size particles. Anytime time you wear off or shear metal from the host body, the atoms and molecules of the wear metals [iron (Fe), aluminum, copper (Cu), Nickel, Manganese, Chromium, Lead, and Tin] go into solution, and the larger particles go into suspension. These atoms and molecules are linearly related to the amount of wear encountered on the surfaces of those metals. It is the detergent-dispersant additive package that determines how much stuff will be held in suspension. Less dense oils (lower viscosity oils) should suspend more material than the higher density (thicker) oils. [ July 22, 2003, 01:38 PM: Message edited by: MolaKule ]

 

[Ray Garlington]

MolaKule said:

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Less dense oils (lower viscosity oils) should suspend more material than the higher density (thicker) oils.

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This seems backwards. Higher density fluids provide more bouyancy per unit volume; therefore, supporting larger particles.

 

[MolaKule]

You're speaking of buoyancy and flotation. It depends on the density of the particles in question. IF the particles are denser than the liquid, then they will sink. If the particles are less dense than the liquid, they should be more buoyant. In a less dense fluid, it should hold more low density particles until saturation. It is the additive package that provides the suspension capabilities for particles greater than "solution" size. Larger and denser particles will, in the absense of turbulence, I.E., fall to the bottom of the sump in still (motionless) oil. For the most part, the Detergent-Dispersant package will suspend the less dense particles that are surrounded by the DD micelle, such as sludge and small metallic particles. I think the thicker oils show more wear because they don't flow as quickly on startup, and they don't cool as effectively as the thinner oils. Anytime you have thinner fluids, the flow rate will be slightly greater with the pressures being equal. The greater viscosity equals a greater pipe restriction, by analogy. [ July 22, 2003, 02:13 PM: Message edited by: MolaKule ]

 

[MikeW]

Less oil making it out to the extremeties of the oiling system (up in the head).

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Originally posted by Dr. T: Can someone point out how you get greater wear with a higher film thickness and strength of oil?

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[Dr. T]

Molacule, some here regard oils such as 0-40, 5-40 and 5-50 as being "thicker oils". Why would these have poorer flow at start-up and contribute to increased wear?

 

[Patman]

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Originally posted by Dr. T: Molacule, some here regard oils such as 0-40, 5-40 and 5-50 as being "thicker oils". Why would these have poorer flow at start-up and contribute to increased wear?

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5w50 Castrol's viscosity at 40C is very very thick, at 110cst. This is double that of many 5w30s! Mobil 1 5w30 for instance, has a viscosity of 53.7cst at 40c, and most other 5w30s are the same, in the 50-65cst range. You can't possibly be telling me that the 5w50 Castrol is going to flow as well in the cold as most 5w30s! The same thing goes with 0w40 Mobil 1, it's pretty thick at 80.3cst at 40c. Redline 5w40 is 94cst at 40c. So even with the 0w and 5w ratings on these oils, they will still not flow as well on startup as a 5w30, 10w30, 0w30 would. Even in the hot summertime I personally would feel uncomfortable having an oil in my engine which is thicker than 70cst at 40C.

 

[moribundman]

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Even in the hot summertime I personally would feel uncomfortable having an oil in my engine which is thicker than 70cst at 40C.

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Patman, Do you know what would be a good cst at the follwing temperatures? Or would the cst be ideally the same at all temperatures? For example <70cst? -30˚C -20˚C -10˚C 0˚C 10˚C 20˚C 40˚C [ July 22, 2003, 04:41 PM: Message edited by: moribundman ]

 

[Patman]

Keep in mind that as the oil gets colder, it's cst increases quite a bit too. Someone posted on here this week as to how the oil thickens up considerably at 0C, -10C, etc. Although each oil would be different, because those 0w oils won't be as thick at -10C as a 10w oil would be. That's where things change around with the 0w oils, they then resist thickening up at the extreme lower temps much better.

 

[Dr. T]

Yes, but 40C is not exactly bone-chilling-the-oil-won't-flow temp. Remember it's almost like 100F. The viscosity will be 2x of a 30 weight because these are hot viscosity temps.. I thought we were talking about cold temp. startup. These are Arizona/Texan temps....certainly they don't need to worry about cold-temp startup wear. ie. At 40C, does it really matter if the the oil flows at say 6"/sec or 8? I don't get all of the logic. Oil filters have a back-flow valve. Oil pressure is almost created immediatly at start-up and there is already (hopefully) oil coating all of the moving parts. How much flow differential matters at a pretty hot 40C? It's only at subartic temps., when parts are already resistant to movement, your fingers are ready to fall off and the battery is near frozen that oil flow matters eg. 5 vs. 15. Even then, the above applies...but certainly an oil that isn't near frozen solid or flows like molasses is preferred. Will a 5-50 flow as well as a 5-30? Sure...it has to (within a certain range) because SAE says so...else it wouldn't be a 5.

 

[JohnBrowning]

First what source is being sited to corralate high viscosity with high wear rates? I have seen just the oposite to be true in my experinces as a Tech. What is being used to judge wear? Are we tearing the engines down or are we useing UOA only? WHat are the engines being used and what are the enviromental counditions..... Based on what I have learned from Terry and Molakule I think that solvency is more important. This assumes that viscosity is at least acceptable for temp. So the thiner weights of oil have greater solvency. If a thicker oil is made more solvent then it's protection propertys should really shine. We could use lube control at a rate of 1-2 onces per quart of oil to test this theroy. Seeing how my Dad runs M1 15W50 in the warm months and 10W30 dureing the winter I can sample his vechiles!

 

[YZF150]

40°C is not a hot viscosity temp. 100°C is a hot viscosity temp.

 

[moribundman]

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40°C is not a hot viscosity temp. 100°C is a hot viscosity temp.

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Well, I think the issue was ambient temp and oil still warming up to operating temperature. Of course ambient temp is also, at least initially, oil temperature. Anyway, if it comes to oil temperatures, I'd say 100˚C is not hot. It's normal operating temperature. 120˚C and up is hot...

 

[Patman]

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Originally posted by Dr. T: Yes, but 40C is not exactly bone-chilling-the-oil-won't-flow temp. Will a 5-50 flow as well as a 5-30? Sure...it has to (within a certain range) because SAE says so...else it wouldn't be a 5.

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But like I said, the 5w50 Syntec is TWICE AS THICK as most other 5w50 oils at 40C, and that temperature is just a little bit hotter than what your oil temp will be in the summertime when your car has been sitting all day. So even right now in summer, when you start your car at the end of the work day, with a 5w50 oil in there it's going to have more startup wear due to the oil being so much thicker than a corresponding 5w30 oil. At much colder temps like -10C perhaps the two oils would be more similar in viscosity, but not at 40C they aren't.

 

[JohnBrowning]

How does one explain thick oil results like Ken4. He can not even find 10W30 and 5W30 is almost impossable to find. 0W30 just started to show up in Singapore. He has been useing 5-15W40-50 weight oils and turning in insanely low numbers. I have the same car made at the same plant and my owners manual recomends 5W30 or 10W30 if 5W30 is not available. I have not seen any thin oil advocates post any numbers as nice as Ken4's without the use of a bypass filter!

 

[Dr. T]

Actually Patman, forget the 5-50...the 10-60 is even more delicious at 40C But on a serious note, I will do a UOA on it but only during the second interval...