Higher Viscosity=better Hydrodynamic film?

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With all else being equal, will a higher viscosity oil provide a stronger hydrodynamic film? For instance, in a high lift cam application, where the oil film is prone to be breached momentarily, will the thicker oil be less likely to allow metal to metal contact? I realize that too thick of an oil will cause problems elsewhere in the engine... but setting all that aside, does the heavier oil have the better hydronamic film? Dan
 
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Depends on how that viscosity is achieved (and measured). Just because an oil is perceived as thicker does not mean it will "provide a stronger hydrodynamic film".
 

fuel tanker man

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That is a good point... thanks for making it. With all else being equal, then, the thicker oil would provide a better film... I would assume (?) Dan
 

fuel tanker man

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You're probably talking about the zinc/phos, and/or the moly... but I don't think it's a moot point in that it would certainly be better for the cam lobes not to have to resort to the barrier additive pack if it wasn't necessary... Which is why I ask the question, would the thicker oil have the better hydrodynamic film, and therefore reduce or perhaps even in some cases eliminate the breaching of the oil film. I'm not trying to make a case for thicker than spec'd oils... I'm just trying to get a better understanding on the relationship between viscosity and thickness of the hydrodynamic film. Dan
 
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All else being equal, a higher viscosity will result in a thicker hydrodynamic film. The relationship is complex, but I can't think of any examples where the trend is not true. Rather than me telling you more than I know, take a look at.... Chew on this awhile and see if it helps you \:\! It takes a little study and but does a decent job of explaining the relationships, particularly the graph.
 
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 Originally Posted By: bruce381
normally YES
With the "all else being equal" clause in place, what would the exception be? I had a nagging little feeling that there would be an exception but couldn't think of it.
 

JAG

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Google this: oil film thickness valve train viscosity newtonian The results of tests and modeling are fascinating and complicated.
 
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 Originally Posted By: fuel tanker man
With all else being equal, will a higher viscosity oil provide a stronger hydrodynamic film? For instance, in a high lift cam application, where the oil film is prone to be breached momentarily, will the thicker oil be less likely to allow metal to metal contact? I realize that too thick of an oil will cause problems elsewhere in the engine... but setting all that aside, does the heavier oil have the better hydronamic film? Dan
My car may not be fully warmed up when I race on to the expressway with the a/c on. At 150f is Pennzoil 10w-40 supposed to form a stronger film than Pennzoil 5w-20?
 

fuel tanker man

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Wiley... that's a great link. And after reading and understanding it, perhaps Harley Davidson really did know what they were talking about when they said synthetic oils would cause bearings to skate (I'm guessing they meant the roller lifters?)... ...so maybe HD isn't as full of beans as some folks (myself included) once thought, with regard to their dis-recommeding synthetic oils for so many years (until Syn3 came out, of course, which might have such an additive as the Cummins and Valvoline techs are mentioning; to raise oil traction). Dan
 
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subscribed. Great links here! Explains a few things to me but I have one main question. Is film thickness proportional to temperature on NEW oil or is it constent given the same senario in an engine? at what temp will say a M1 0W-40 become like their 5W-30 when new? It may never, I'm just asking bc I didn't read word for word on the zddplus techbreif but I didn't pick this up.. . I know that overtime an oil shears out. Thanks
 
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Viscosity is temperature based, not so much time, although 'external factors' can affect it. Such as; Fuel contamination, mechanical shear, oxidation, thermal or acidic breakdown. Though this list is not all inclusive.
 
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M1 0W40 is [email protected] and has a VI of 186, A random conventional 5W30 is [email protected] and has a VI of 158. Using this information, we can calculate that Mobil 1 0W40 will be as thick as conventional 5W30 when it hits 115C(239F). What this means is M1 0W40 at 239F is as virtually the same thickness as conventional 5W30 at 212F.
 
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Oil film thickness (OFT) increases with increasing viscousity and speed and with decreasing load whether it is hydrodynamic or elasto-hydrodynamic (boundary) lubrication. In short, yes, the film thickness will increase with increasing viscosity (within limit. Not to the extend where the oil cannot flow at all) in all parts of engine except at top piston ring which is currently being debated here.
 

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In this era of specialized polymer additives, this may no longer be true, since certain FM and AW polymers resist compression and shear in very thin base oils.
 
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