thick and thin and perspective

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Oh no, another redundant thick/thin thread. Maybe, but I want to start fresh with a re-framed argument. I ask that you try to play along for a moment. All right, I'll accept that an oil can be too thin. At that point, I begin to imagine a bell curve with an ideal viscosity for a given add package and a given application/engine. So, I have to also grant that an oil can be too viscous. Ok. Oil can be too thin and oil can be to thick. The real discussion then is how do we tell (for a given add package and given application) when an oil is outside the acceptable range. Since there will never be consensus on how much wear is acceptable, let's say that we seek the viscosity that produces the peak of the curve (in this case the curve describes the lack of wear, otherwise it would be a valley representing the lowest wear). I recognize that this value will be confounded with many other things - peak and average load, temp, and rpm, fuel, behavior, engine, add package, ect. For this discussion, let's try to accept that something like acetone would be too thin to use as a base for an engine lubricant and that tar/asphalt would be too thick. Let's also accept that a frictionless lubricant will not be found and that a balance between wear and fuel economy is a personal preference and is not a part of the question. How do we find peak of the bell curve? How do we describe it? Is there reason to believe that the bell curve is some other shape? Is there a thresh hold on each end that will produce some sort of nearly square-wave shape instead of a bell? If we use a base that is very polar and electrostatically sticks to the metal will we get a different answer to the question? Anyone willing to begin...
 
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I like how you framed the question. In particular this part:
quote:
I recognize that this value will be confounded with many other things - peak and average load, temp, and rpm, fuel, behavior, engine, add package, ect.
I believe we see people pointing to a moderately high loaded engine at high temperature and then basing their conclusions on only this operating scenario. Generally, most passenger car/truck gasoline engines will spend at most 5%-%20 of there operating time under these conditions. Kinda' reminds me of a time I was mentoring a young engineer on FI maps. I had the hardest time explaining to him that engines don't run WOT all the time. Diesels where peak HP/Torque RPMs are much lower and the components tend to have much more mass presents another set of conditions also.
 

GMorg

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I think that we can define the high limit by pumpablity (can we get the lube to where it is needed) and tendency to cavitate. Apparently these parameter can be calculated for a given bearing. I assume that we must limit ourselves to the weakest link. The tightest bearing and the maximum pump output. So how to we find the low end. Trial and error? Can we get an objective but useful calculation of film strength?
 
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Since it varies based on specific application, temperature ranges, etc. You would have to take, for example, two oil changes throughout the summer with different grades of oil and see which produced less wear. If it's not a significant difference, then it simply just isn't significant. I am getting the feeling that when we see great results with 20w-50 oils and great results with 5w-20 oils that viscosity doesn't seem to matter much. In my car I have a synthetic 5w-30 in it, but my next OCI will probably be using a synthetic 50 weight in it to compare wear and UOA results. It will be a bit scewed in the end because of oil consumption but it's all trial and error and engine and condition specific. Who knows the 5w-20 specified engines might end up with rapidly increasing wear when they reach high mileage that a thicker oil will reduce, this seems to be an unknown at this point.
 

GMorg

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MN Driver, It sounds like you are saying that there may not be any commercially available oils that are too thick or too thin. I think that since the "thin logic" crowd (term of endearment) generally uses data that represents averages and/or cumulative damage, that they would agree. Keep in mind though that from W20 to W50 at operating temps, there is only about a two fold range of viscosities. Where as, for your 5W30 there is likely a 10 fold range between startup and operating temps on a hot day. Is is possible that the thick/thin debate (for a given engine, drive, add pack, ect.) only applies to startup? I would argue that even under load and at high temps that the viscosity difference between w20 and w50 will still be too low to matter. However, I know that I am guessing and cannot back-up that positon. If I did know the answer, I suppose that I would not need to participate in this discussion. So, is the thick/thin debate a startup question? I seem to recall that it is the extremes of load and temp where the "thick heads" (again, term of endearment) tend to concentrate.
 
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Thanks for the examples, that answered quite a bit of what I was trying to figure out. GMorg, I believe that the thick headed argument where the extreme conditions come up is where people drive hard when it's hot or tow heavy loads, I couldn't imagine a 250 degree sump while towing on a day above 100 degrees, at some point, albeit it would be very heavy loads and high temps, the viscosity could mean the differnce between their engine seizing during those condititons making the issue between PPM wear to be irrelevant. I think it's more unlikely than many think but I have a feeling that the thick side of the argument has something along these thoughts in mind. I've driven mine very hard and in some cases high speeds on the freeway on hot days and the changing sounds of the engine make me want to boost my viscosity a bit. It's easy to think that thicker is better with such an experience, in my case I'd like to give it a shot with similar experience and see how things compare. Once taking a 2 hour highway trip at about 70 mph and then climbing up a few large hills I lost 1/4 quart, normally it takes me 500 miles at the very least to lose that much oil, viscosity must have encountered a massive drop with high heat to lose oil like that.
 
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quote:
Originally posted by GMorg: I think that we can define the high limit by pumpablity (can we get the lube to where it is needed) and tendency to cavitate.
I agree with high limit as pump ability is a major factor. I can't help but wonder how much of a role would engine load, engine horsepower, crank shaft flexing, and bearing speed in SFPM, place on the low limits demands of oil film. Example such as a lighter weight 166 HP 4 cylinder Honda car on near level ground vs a 4500+ pound truck with a 300 HP V8 towing a boat up a mountain pass. Obviously the Honda does well with 5w 20 in UOAs posted on this board. But I'm having a hard time grasping the concept that a 5w 20 would be the best choice for more extreme conditions. Such as towing a boat with a pickup up a mountain pass. Got lots of big hills around here in the Northwest hence the more extreme example.
 
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quote:
Originally posted by GMorg: MN Driver, Is is possible that the thick/thin debate (for a given engine, drive, add pack, ect.) only applies to startup? I would argue that even under load and at high temps that the viscosity difference between w20 and w50 will still be too low to matter.
I agree, that the differences upon reaching operating temperature are small.
quote:
So, is the thick/thin debate a startup question? I seem to recall that it is the extremes of load and temp where the "thick heads" (again, term of endearment) tend to concentrate. [/QB]
I think that the "thin" guys like the effeciency in the first 15 minutes of a trip and overall more effecient operation under daily light loads while the "thick" guys like the the high temperature high load protection for the situations they do or might encounter in their application. What someone considers their priority determines their camp. Both sides have valid arguments.
 
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quote:
Originally posted by Hirev: I can't help but wonder how much of a role would engine load, engine horsepower, crank shaft flexing, and bearing speed in SFPM, place on the low limits demands of oil film. Example such as a lighter weight 166 HP 4 cylinder Honda car on near level ground vs a 4500+ pound truck with a 300 HP V8 towing a boat up a mountain pass.
In either case, each engine puts out a maximum amount of HP/Torque. All one can due is vary the amount/quantity of load.
quote:
Apparently these parameter can be calculated for a given bearing.
That adddresses the bearings, but what about all the other components and the different lubrication regimes they operate in?
 
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2.35L 160hp/160ft-lb 3300 lbs + 800 lbs pass/luggage = 4100 lbs 5.4L 300hp/365ft-lb 5100 lbs + 4700 lbs trailer = 9800 lbs 5.4L/2.35L x 4100lbs = 9421lbs Proportionally, not much of a difference.
 
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That looks like a good reason to plus one the Honda oil grade if you are going to drive around with 4 x 200 pund men all the time..Poor Honda. Fuel mileage is going to take a dive from all the weight, might as well keep things in "proportion".
 
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That was suppose to reflect a driver with 3 passengers and luggage. And according to the Centers for Disease Control and Prevention, more than 60 percent of Americans are overweight and of these, more than 30 percent are obese, so I thought I made a fair assessment. [Big Grin]
 

GMorg

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Above, 427z06 provided links that illustrate equal to lower wear on low viscosity oils. Redline presents data on their website that wear is lower with their 40 weight than with their 50 weights. So, in addition to better flow (not in dispute), higher HP (seems clear to me), and better economy (some times), lower viscosity can result in lower wear, maybe. That leaves the thick crowd with the argument that thick is better at preventing catastrophic failure. However, my original question was trying to get at how we find the limits. Where is too thick and too thin? We have identified a few examples of how to find too thick. How do we find the limits of too thin?
 

JAG

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All that is needed to prove that a UOAs are not always accurate "wear-ometers" is just one example of severe engine wear occuring which was determined by engine teardown while the UOAs (taken periodically throughout the test) did NOT show the wear metal concentrations increasing at an alarming rate during the time the true wear rate spiked. I saw this in one of the engine/oil studies that someone linked in another viscosity thread. Sorry I didn't go searching for it to provide the link...perhaps someone remembers it...the oil was quite thin and produced massive valvetrain wear toward the end of the test. Other than taking apart the engine and measuring dimensional changes of parts, I think that having particle counts of the VOA and the UOA for an oil will provide a much more accurate measure of relative engine wear. Subtract the # of VOA particles from the UOA particles for each size range to calculate the # of foreign particles for each size range that ended up in the oil. Then come up with a weighted total by summing the # of FOREIGN particles in each size group times the average size of each group. For example: Sizes of 1-10 microns: 1000 Sizes of 10-20 microns: 500 Sizes of 20-30 microns: 100 Weighted Total would be: 1000*5+500*15+100*25 = 15000. This number would most closely have units of volume. Pick the winner of oil A vs oil B by whichever one has the lowest weighted total. That's a start for us amatuers. I'm sure tribologists already have this figured out and have a much better method, but this is my attempt. But the engine should be "clean" prior to testing oil A vs oil B because one of the oils could have a stronger detergent/dispersant package than previous oil fills and clean out some lodged debris from a previous oil, which would artificially inflate its particle counts. Another method would be to dissolve the particles caught in the oil filter which could provide an indication of the size and quantity of larger wear particles. I think that the point that GMorg made about startup wear is excellent. The difference between 10 cst and 12 cst at full operating temps pales in comparison to 100 cst vs 175 cst which can occur between different oils at much colder temps. I think that this is where thick oils can really stink in some engines. A magical oil that has a constant viscosity as a function of temperature sure would be an awesome invention and I think the viscosity of it could be chosen differently (thicker at operating temps) in some cases than is currently done for oils. That (warmup viscosity) is one factor that seems to save thin oils from being a totally bad idea. Another is the property of oils in which they increase in viscosity as the pressure on them rises very high (Newtonian vs non-Newtonian fluid). [ March 16, 2006, 11:51 AM: Message edited by: JAG ]
 
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Engine 2.5 TDi, V6, 148125 miles. Car 2001 Audi Allroad. Used VW approved longlife diesel oil. Longlife OCI 18750 miles.
 
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