Hey guys,
Is it possible for a straight weight oil to shear? If so how would that work?
Is it possible for a straight weight oil to shear? If so how would that work?
straight weight shearing?
- Thread starter Max_Wander
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I've seen a big dose of Chevron ProGuard shear Chevron Dello 400 40w oil. I think ProGuard is a good product but should be use in the tankful just before your next oil change.
Bruce, a straight grade PCMO in an engine is going to have virtually no permanent vis loss due to shearing, correct? That was my point. Any permanent loss in viscosity will be the result of fuel dilution, not mechanical shearing as with a multi-vis oil loaded with polymeric VI improvers.
Even a straight weight oil contains polymer chains that can be mechanically stressed and broken, however not to the extent that VIIs can be sheared. I believe this is what Bruce is referring to.
Good answer. A+ . End of conversation.
Quote:
No it isn't.
What are these "polymer chains"? (I'm not a chemist).
Back of the class, no not next to THOSE girls....sorry sudden flashback......
He is referring to the base oil....oils are polymer chains.
""chemical attack - which can cause polymer chains to break down and shear.""
Love to see some published papers (perhaps I'm behind the times) on this IMHO there is not really chemical shear but more of a "solublizing" of the polymer keeping it "coiled" but maybe so please post a source for this.
""Even a straight weight oil contains polymer chains that can be mechanically stressed and broken, however not to the extent that VIIs can be sheared. I believe this is what Bruce is referring to.""
Id say not Polymer but any high molecular wt fractions in the oil are subject to and WILL shear the longer the chain lenght in the more shear can take place, more noticiable in high vis gear oils not so much PCMO's, as I guess only a few percent vs a lot more with a VII PCMO
Bruce
Love to see some published papers (perhaps I'm behind the times) on this IMHO there is not really chemical shear but more of a "solublizing" of the polymer keeping it "coiled" but maybe so please post a source for this.
""Even a straight weight oil contains polymer chains that can be mechanically stressed and broken, however not to the extent that VIIs can be sheared. I believe this is what Bruce is referring to.""
Id say not Polymer but any high molecular wt fractions in the oil are subject to and WILL shear the longer the chain lenght in the more shear can take place, more noticiable in high vis gear oils not so much PCMO's, as I guess only a few percent vs a lot more with a VII PCMO
Bruce
As I said, I'm no chemist but this makes more sense. Calling the HC chains "polymer" didn't make sense to me.
I still stand by what I said: A straight PCMO is going to suffer virtually no vis loss from mechanical shearing. A heavy gear oil being chewed up continually by gears I can see.
G man I agree
""I still stand by what I said: A straight PCMO is going to suffer virtually no vis loss from mechanical shearing. A heavy gear oil being chewed up continually by gears I can see.""
But any liquid can shear if "ground up". But for most use in a IC engine not really a problem.
bruce
""I still stand by what I said: A straight PCMO is going to suffer virtually no vis loss from mechanical shearing. A heavy gear oil being chewed up continually by gears I can see.""
But any liquid can shear if "ground up". But for most use in a IC engine not really a problem.
bruce
alright this is good info! "polymers shear much easier than hydrocarbon chains, and longer chains of either shear more readily than smaller ones."
i'm sold!
i'm sold!
I guess we are talking semantics. A hydrocarbon chain is a form of a polymer in the loose sense of the word. Technically an oil, a hydrocarbon chain, is an oligomer.
http://www.m-w.com/cgi-bin/dictionary?sourceid=Mozilla-search&va=polymer
http://www.m-w.com/cgi-bin/dictionary?va=oligomer
http://www.m-w.com/cgi-bin/dictionary?sourceid=Mozilla-search&va=polymer
http://www.m-w.com/cgi-bin/dictionary?va=oligomer
I think engine parts can permanently shear oil (pure oil). Oil pumps shear oil. Timing chains shear oil. Timing gears shear oil. Ring/cylinder interfaces shears oil. For sure some oils are much more shear resistant than others.
I think oil can shear chemically as well, very near the combustion chamber small amounts of oil are subject to oxidation (chemical burning) on the cylinder walls and piston lands. Some of the results of this combustion call for AutoRx!
I think oil can shear chemically as well, very near the combustion chamber small amounts of oil are subject to oxidation (chemical burning) on the cylinder walls and piston lands. Some of the results of this combustion call for AutoRx!
Are higher viscosity oil molecules (say for gear oil) physically larger than the molecules for lighter vis. oils (like PCMO)? If so, I would think it would be easier to tear them apart.
Pablo, certainly some shearing takes place with a straight weight. The point is the effect is negligible. Not so with a multi-grade where the operating vis is almost totally the product of VI improver. When those polymer molecules get chewed up, the effect can be drastic.
A single hydrocarbon molecule (or any molecule) is called a 'Mer'. Poly just means many, so when you put these molecules in a 'chain' you have "many mers" or Polymer. Any molecular bond can be broken but requires energy to be put into the system such as heat, mechanical, chemical, etc. Polymer lengths plays a role viscosity. I don't know for sure but I would imagine the bond strength of the oil polymers are stronger than that of VI improvers. I believe that is the point G-Man is making but the others guys are right also, an oil chain can 'shear.'
The bottom line is that in the absence of something as fuel dilution the only problem in regards to viscosity will be oxidative thickening in a straight 30 grade oil.
A model may go as this:
Over a time period the oxidative thickening will increase the viscosity from a 30 to a 40 wt. oil in a straight grade 30 oil.
For a 0W30 grade oil with viscosity improvers the oil may thin first to a 25 grade then thicken to a 35 grade over the same time period.
I would choose the later as the average viscosity would be 30 over time, assuming this is your desired viscosity from the start.
aehaas
A model may go as this:
Over a time period the oxidative thickening will increase the viscosity from a 30 to a 40 wt. oil in a straight grade 30 oil.
For a 0W30 grade oil with viscosity improvers the oil may thin first to a 25 grade then thicken to a 35 grade over the same time period.
I would choose the later as the average viscosity would be 30 over time, assuming this is your desired viscosity from the start.
aehaas
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