Is Viscosity the Least Important Aspect of a Oil?

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I have beeen having very heretical thoughts... Is it possible that viscosity could be the least important factor in an oils design instead of the most? Is it possible that a quality 0W20 Synthetic could outperform a generic 20W50 Dino in most vehicles? And vice versa a quality 15W50 synthetic would outperform a generic 5W30 Dino? I realize that each engine design will have a ideal viscosity for any given oil temp but no oil can be ideal for all temps. I really am starting to wonder given swings from 5W20 to 20W50 sometimes for the same temperature depending on the local political climate and marketing realities. Gene
 
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Gene, I must confess to similar thoughts at times, about the wonder of additives, and "wonder additives" themselves. Pure hydrodynamic lubrication involves no contact, and minimal additives. I look after turbines with rotors that weigh 30 tonnes, spin 3000RPM, and run 12 years (8,000 hours per year) between overhauls. Most times, we don't even change the white metal bearings. ISO 32 oil (about 10W, or ATF) does the job marvelously, with next to no additives. When things start touching, the additives save the day. Dunno what the ideal engine viscoscity is, however.
 
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Viscosity is critically important. It is the first line of defense to prevent wear. If an oil is designed with too thin of a viscosity (perhaps 5w20 would qualify here), then more additives and/or a higher quality base oil are needed to compensate. Of course some level of antiwear additives is desireable in all motor oils as a second line of defense.
 
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No. I always thought that "the pro's" touted that viscosity is by far more important than either type or brand of motor oil.
 
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The turbine analogy is dangerous in the car context. A piston/reciprocating engines do at least two things a turbine does not. First, they create huge perpendicular loading from the con rod against the crank journal bearing. A piston engine oil must be able to keep these parts separated on the power stroke. Second, the oil must be able remain functional despite continuous contamination from blow-by gasses from the combusion process, which in turn, influence actual viscosity.
 

Gene K

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quote:
Originally posted by cryptokid: yeah right, put a 0w5 in a viper and run it around the track. be sue to tell us how long the engine lasts.
Already been done. There is a 0W5 Racing Oil for that specific purpose. Gene
 

Gene K

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quote:
Originally posted by Pablo: Listen - oil can almost be thought of as a system. One link is not right and it doesn't perform...no matter how much humans wrap rationalizations called words around it....viscosity is important as are a list of other attributes. It may have lost some significance in the minds of certain humans, but that doesn't necessarily change it's importance.
I realize vicosity is important I just wanted to point out that there is a lot more to a oil than vicosity. If I was given a choice between a bottle that just says Motoroil 10W40 at the local convienience store and Mobile 1 0W20 I know which one I would choose for a 10,000 ML OCI. Gene
 
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Film strength might be the most important characteristic of an oil. Other things being equal, higher viscosity oil will have higher film strength (other things being same base oil, etc., etc.) Viscosity being equal, PAO base oil has a higher film strength than petroleum oil. Turbines and all bearings have the bearing sized to carry the load. A turbine running ISO32 oil (~10 wt.) will have by design larger bearings with more bearing surface area than turbines designed for ISO100 oil (~30 wt.) One brand of diesel engine I've worked on, Sulzer, has water cooled pistons on some models. In order to make room for the piston cooling water telescoping pipes, the crosshead (like a wrist pin) is smaller than desired. To handle the load on these undersized bearings, special oil booster pumps increase the oil pressure to these bearings. Later models of these engines with oil cooled pistons has much larger crossheads with much larger bearings and no need for the expensive booster pumps...all are using similar 30 wt. crankcase oil. Ken
 
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Listen - oil can almost be thought of as a system. One link is not right and it doesn't perform...no matter how much humans wrap rationalizations called words around it....viscosity is important as are a list of other attributes. It may have lost some significance in the minds of certain humans, but that doesn't necessarily change it's importance.
 
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The turbine example was that in an environment in which the load was constant, and hydrodynamic lubrication is assured, then additives mean little. In spite of huge weights, high surface speed, and low viscoscity.
 
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quote:
Originally posted by Gene K: If I was given a choice between a bottle that just says Motoroil 10W40 at the local convienience store and Mobile 1 0W20 I know which one I would choose for a 10,000 ML OCI.
[Off Topic!] I wouldn't use the bottl that said "Mobile 1" either. [Wink]
 
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quote:
Originally posted by Gene K: If I was given a choice between a bottle that just says Motoroil 10W40 at the local convienience store and Mobile 1 0W20 I know which one I would choose for a 10,000 ML OCI.
I think I would mix the two, leaning more heavily on the 10w40, drive easy until I get somewhere that has decent oil, change it out, and call it a flush!
 
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Molakule, yep, it's cooled to about 50 degrees, and filtered to about 20 microns. The oil feed to the bearings is into the top (unloaded) area, and it forms it's own wedge. It's pressurised to 20MPa and injected into the loaded side (bottom) of the bearings for start-up, and speeds up to 400RPM. Above 400RPM, the bearings take care of themselves.
 

MolaKule

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You need a specified viscosity at operating temperature to provide a minimum oil film thickness. So in my view, visocsity comes first with the AW add package coming in second in importance.
 
I've wondered the same thing, Gene. And while there's lots of good points made in this discussion, I don't hear much proof of the criticality of viscosity. I've mainly started to wonder about this since the same car will specify radically different viscosities depending on the the country (not the environment). Is there any chance that the criticality of viscosity is a left over from when oils broke down much more easily than they do today?
 

Gene K

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quote:
Originally posted by MolaKule: You need a specified viscosity at operating temperature to provide a minimum oil film thickness. So in my view, visocsity comes first with the AW add package coming in second in importance.
That is fine in theory, but what does it mean? Let us take a DOHC 2.0L-4, 3.0L-6, 4.0-8 or 6.0L-12 with typical clearances and a 7000 rpm redline; What vicosity would be required at 100C (212F), 125C (257F), and 150C (302F) respectively? How does this relate to in the real world? 20W, 40W, 60W? Gene
 

MolaKule

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But Shannow, isn't that oil highly pressurized, filtered, and cooled. I helped design a Nuclear plant one time and the electrical power generating turbines (horizontal steam, axial design) ran at 1800 RPM (I forget the total I or moment of inertia) with an oil pressures of 100 psi with the incoming oil temp at 40-60 F. The turbines were axial flow and had large bearings resting in Pillow Blocks. The split bearings were 0.375 m in radius and 0.45 m wide. They looked to be about 8 cm thick. This turbine oil had special additives to combat oxidation, moisture, rust, and EP and AW agents. Basically, it was a synthetic AW hydraulic oil of about ISO 46. They never changed the oil. The Operating Engineers would sample oil on the fly and add additives or makup oil according to analyses. The oil filters were contained in large tanks and were removable, screen-mesh, resusable types.
 
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