Optimal kinematic viscosity for mimimal wear?

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With all the talk on thick vs thin (i.e. 20 wt or lighter oil) I've always thought there must be a definitive scientific answer. It's universally accepted that 90% of engine wear occurs at start-up when all oil (except qualifying oil) is too thick with the kinematic vis in the 100's or even higher when very cold. Many claim the ideal vis coincides with a 30 wt oil at normal operating temp. So that would translate to 9.3 cSt to 12.5 cSt. Widman goes along with this, suggesting wear increases in both directions outside of this range. With synthetic oil, many say it's no problem with oil temp's up to 300F and you don't need a to go to a heavier grade of oil. (GM 4418M). That translates into a viscosity under 4 cSt. Joe Gibbs Racing concurs with that, saying a vis as low as 5 cSt or even 4 cSt will not result in excessive wear and that of course is at full power. I think the answer is it depends. That yes, with the best syn oils and their advanced ad' pac's you can go as low as 4 cSt in engines with tight clearances and no particular lubrication issues. But the main issue remains having the lowest possible vis at start-up.
 
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I don't agree that 90% of engine wear occurs on Start up. I think more wear happens on a cold-start up after an engine has been sitting, but I don't think 90% is accurate. This is JME from all the engines I have driven and ones that I have torn a part knowing their history. I would say 30% is from start-up and 70% is from driving/idling the engine. Again JME. ;\) Aside from that I would think that you could cut down the start-up wear using a thinner oil like a 20wt versus at 30wt, so long as your Manufacturer says its suitable for your operating conditions/climate.
 
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 Quote:
It's universally accepted that 90% of engine wear occurs at start-up..
Reference check please. 9.3 cSt to 12.5 cSt? I don't think the window is quite that narrow - and I think it's not a one sided equation. It depends on the size and shape of the wear surfaces.
 
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 Originally Posted By: StevieC
I don't agree that 90% of engine wear occurs on Start up. I think more wear happens on a cold-start up after an engine has been sitting, but I don't think 90% is accurate. This is JME from all the engines I have driven and ones that I have torn a part knowing their history. I would say 30% is from start-up and 70% is from driving/idling the engine. Again JME. ;\) Aside from that I would think that you could cut down the start-up wear using a thinner oil like a 20wt versus at 30wt, so long as your Manufacturer says its suitable for your operating conditions/climate.
You know, I have to agree with that.
 
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I think the parameters are to narrow. Many engines will do very well on a broad range of viscosities. Thicker oils do not need more clearance and the oppossite is true as well. This is a myth. SOme engines can have virtually no wear with a 20wt while others need a 60 wt or they have lubrication failures (think BMW M3). The best thing to do is go by the manufacter recomendations for your vehicle for your conditions and the area you live in (fuels and product availablity is taken into account. If you own a car that says 5w20 exclusively where you live then use 5w20. It is optimal with the oil specs recomended. If you own one of those BMW's that require a 60wt to stay together.. I wouldn't try to run GC (0w30)in it. This is following instructions 101. The only folks who should dictate what viscosity is optimal is those who build and blueprin t their own engines. With this type of craftsmanship (I consider it an art in some cases) these builders are going to be very conservative in what oil they want that engine run on.. I don't blame them. They don't have the budget to R&D thinner and thinner oils like a manufacterer or a major race team does to make it work.
 
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Lets just clarify that the start up wear (a real phenomenon easily demonstrated in a lab) is related not to lack of lubrication, but to the cold engine problem. Water condenses on cold cylinders and combines with combustion byproducts forming carbonic and sulfuric acids. That produces chemical wear and not a mechanic wear. This is why synthetic oils may fall short in corrosion protection as being more viscous in room temp, they will run down and expose metals. Maybe this is why Mobile 1 produces more iron on UOA? Then, lets answer the original question. The optimal wear is achieved with heavier rather than thin oil. The heavier oil will separate moving parts better than thin oil under pressure conditions. The reason thin oils are utilized successfully, is that ZDDP and other additives prevent excessive wear under full metal contact seen in thin oil under pressure (valve train). Thin oils provide better fuel efficiency as they decrease friction at the ring/cylinder interface at the expense of minor increase of friction in valve train and a potentially higher wear under heavy load and high oil temp. Notice that 18 wheelers use 15W40 rather than 0W20. The example of racing is poor as as racing is all about max power at the expense of wear. Racing engines are torn down after each race and rebuilt.
 
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 Originally Posted By: friendly_jacek
Lets just clarify that the start up wear (a real phenomenon easily demonstrated in a lab) is related not to lack of lubrication, but to the cold engine problem. Water condenses on cold cylinders and combines with combustion byproducts forming carbonic and sulfuric acids. That produces chemical wear and not a mechanic wear. This is why synthetic oils may fall short in corrosion protection as being more viscous in room temp, they will run down and expose metals. Maybe this is why Mobile 1 produces more iron on UOA? Then, lets answer the original question. The optimal wear is achieved with heavier rather than thin oil. The heavier oil will separate moving parts better than thin oil under pressure conditions. The reason thin oils are utilized successfully, is that ZDDP and other additives prevent excessive wear under full metal contact seen in thin oil under pressure (valve train). Thin oils provide better fuel efficiency as they decrease friction at the ring/cylinder interface at the expense of minor increase of friction in valve train and a potentially higher wear under heavy load and high oil temp. Notice that 18 wheelers use 15W40 rather than 0W20. The example of racing is poor as as racing is all about max power at the expense of wear. Racing engines are torn down after each race and rebuilt.
Very nice post!
 
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 Originally Posted By: friendly_jacek
This is why synthetic oils may fall short in corrosion protection as being more viscous in room temp, they will run down and expose metals. Maybe this is why Mobile 1 produces more iron on UOA?
Bogus information alert!!!
 
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 Originally Posted By: Pablo
 Originally Posted By: friendly_jacek
This is why synthetic oils may fall short in corrosion protection as being more viscous in room temp, they will run down and expose metals. Maybe this is why Mobile 1 produces more iron on UOA?
Bogus information alert!!!
My thoughts exactly! Simply BOGUS!
 
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friendly_jacek. You have some good points. I don't like thin oil's period. I don't care about fuel mileage. I care about engine protection. The best viscosity in my opinion for minimal wear are the Euro A3 0/5w30 oil's. I now have two GM cars with Ecotec engines (2.2 & 2.4). Over in Europe these engines require A3 5w30 oil meeting the GM-LL-A-025 specs with a higher viscosity than the oil's found in North America.
 
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 Originally Posted By: friendly_jacek
The example of racing is poor as as racing is all about max power at the expense of wear. Racing engines are torn down after each race and rebuilt.
Wrong. In a 17 race season, a Formula one driver is allowed 8 engines. These engines are sealed prior to and after events. They may not be rebuilt.
 Quote:
After consultation with the relevant engine supplier the FIA will attach seals to each engine prior to it being used for the first time at an Event in order to ensure that no significant moving parts can be rebuilt or replaced. Within two hours of the end of the post race parc ferme exhaust blanking plates (with one 10mm diameter inspection hole per cylinder) and further seals will be applied to all used engines in order to ensure that these engines cannot be run between Events. Upon request to the FIA these additional seals will be removed after the start of initial scrutineering at the next Event at which the engines are required. All such engines must remain within the team's designated garage area when not fitted to a car and may not be started at any time during an Event other than when fitted to a car eligible to participate in the Event.
 
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 Originally Posted By: Pablo
Bogus information alert!!!
Do you have proof that the information I posted is incorrect? Yes, synthetic oils have corrosion inhibitors in them, but base oils have inferior corrosion resistance. At least I have some evidence for my claims: "Rust protection is achieved by metalworking fluid containing mineral oil. Synthetic lubricants do not provide proper corrosion protection." from http://www.substech.com/dokuwiki/doku.php?id=cutting_fluids_coolants "Rust protection oils are commonly based on mineral oils (either paraffinic or naphtenic)." from http://www.substech.com/dokuwiki/doku.php?id=rust_protection_oils
 
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 Originally Posted By: friendly_jacek
Lets just clarify that the start up wear (a real phenomenon easily demonstrated in a lab) is related not to lack of lubrication, but to the cold engine problem.
Two questions. First, what's the basis for this? Second, what about the problem of the engine, even if briefly, turning over with little or no oil pressure? Yes, there are the residual EP and/or AW components that should still be on the metal, but this is still going to be a very challenging interval until pressurized oil arrives on the scene, so to speak. Another thing to consider: the Toyota hybrids, which do a lot of of/off with the gas engine actually use the smaller of the two motor-generators to spin the ICE up to about 1k rpms before the ECU adds fuel and spark. In effect, the engine pre-oils itself before it takes on a load. Why bother with this mechanism if start-up wear is not related, at least in part, to lack of lube? Beyond that, why would there be any market for pre-oilers, which of course, are meant to deliver oil pressure to the bearings before you start your engine? Beyond that, why would there be any need for assembly lube compounds for new or reassembled engines?
 Originally Posted By: friendly_jacek
Water condenses on cold cylinders and combines with combustion byproducts forming carbonic and sulfuric acids. That produces chemical wear and not a mechanic wear. This is why synthetic oils may fall short in corrosion protection as being more viscous in room temp, they will run down and expose metals. Maybe this is why Mobile 1 produces more iron on UOA?
MAYBE, if an only if you start the engine, and then shut it right down. If you run the engine, sure, it takes the whole engine a bit to rise to operating temps, but I can't see the very hot combustion gasses allowing anything, other than perhaps the oil film, to remain on the cylinder walls for more than a couple seconds. I'm with Pablo on this one...
 Originally Posted By: friendly_jacek
Then, lets answer the original question. The optimal wear is achieved with heavier rather than thin oil. The heavier oil will separate moving parts better than thin oil under pressure conditions. The reason thin oils are utilized successfully, is that ZDDP and other additives prevent excessive wear under full metal contact seen in thin oil under pressure (valve train). Thin oils provide better fuel efficiency as they decrease friction at the ring/cylinder interface at the expense of minor increase of friction in valve train and a potentially higher wear under heavy load and high oil temp.
The use of vague, subjective terminology ("thick" or "thin") reveals the flaw in this. You simply can NOT generalize in this way using such vague terms. The most effective lube, in terms of viscosity, is what works best in any given engine. If you drive a BMW M series car, then 10w-40 or 20w-50 is a dangerously "thin" oil. If you drive a Honda Accord or Toyota Camry, then 30, 40, and 50 wt oils are thick beyond optimal. And your reasoning about "thin" oils being used successfully because they contain EP/AW additives also does not fly. By this reasoning, you would need no such additives in your "thick" oils. But of course, they are most surely there. You also can not generalize that "thicker" oils (whatever those are) do a "better" job separating moving parts than thin oils under "pressure conditions." Oil, like all liquids, is a non-compressible fluid. If a car is designed for, and in proper condition so that it keeps the right amount of oil, in the right place (bearings), and at the right pressure, a "thin" oil will keep parts separated as well as a "thick" one. Obviously, it gets much more complicated than this in the real world. Many factors all come together to determine whether a particular oil will work in a given application. Viscosity is just one of those.
 Originally Posted By: friendly_jacek
Notice that 18 wheelers use 15W40 rather than 0W20.
I also notice that apples look, smell, taste, and feel different from oranges. It's simply a different lubricating context. They are operated differently, geared differently, frequently under heavy loads, and run in a totally different rpm range. Are you recommending that I use 15w-40 in my Camry, which specs 0w-20 as the primary vis? Here's a good place to repeat my favorite broken-record question: if these "thin" oils (OK, let's just say 20 wt for now) are comparatively poor compared to thick oils then, almost a decade into their broad-based use, where are all the damaged engines? And if you want to make the general claim of inferiority for thin oils, here-and-there anecdotes don't cut it -- there would have to be a general pattern -- and there just isn't.
 Originally Posted By: friendly_jacek
The example of racing is poor as as racing is all about max power at the expense of wear. Racing engines are torn down after each race and rebuilt.
Ah, now here's something that we are in full agreement about.
 
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 Originally Posted By: friendly_jacek
. . . At least I have some evidence for my claims: "Rust protection is achieved by metalworking fluid containing mineral oil. Synthetic lubricants do not provide proper corrosion protection." from http://www.substech.com/dokuwiki/doku.php?id=cutting_fluids_coolants "Rust protection oils are commonly based on mineral oils (either paraffinic or naphtenic)." from http://www.substech.com/dokuwiki/doku.php?id=rust_protection_oils
But this is a totally different context. Beyond the fact that we're talking about metal and rust/corrosion, everything else involved is different. Successfully altering metal from one form to another, and successfully containing internal combustion are very different things.
 
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Where's the article that stated that increasing the HTHS up to something crazy like 11 or 16 reduced wear with each increase... And come on guys with this whole thing about bearings and cylinders hanging on till the oil pressure arrives. Oil pressure isn't more than half a second behind the first revolution of the crank.
 
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