Impact of Lubricants on Engine Friction and Durability

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JAG

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Here's a nice set of slides by Ian Taylor. I think the most interesting ones are about the impact of Lubricants on Oil Film Thickness. Note the film thickness being a function of the square root of the oil viscosity. Doubling film thickness requires quadrupling the viscosity in such cases.
LINK to slides
 
At the end Taylor mentions we would have to ensure the oil had adequate durability. The paper was about reducing friction and the reduced fuel consumption that comes from that, resuting in lower CO2 emissions, and was not about durability.

So what is " adequate durability " ? From various sources on the internet, fewer than 1.2 % of vehicles achieve 200,000 miles, for all sorts of reasons, engine wear out being just one of them. Pretty clear to see that making an engine last 200,000 miles would be " adequate durability" for an auto manufacturer. Actually, that number could even be lower. Would auto manufacturers care if 5% of their engines wore out and became knocking, oil burning heaps prior to 200,000 miles?

From postings I've read, most bitgoers want more than 200,000 miles out of their engines, although I wonder how many sell their vehicle before then. I would like to see 300,000 miles on mine, and I'm closing in on 200,000 miles in a year or two. This is on a Suburban I keep for towing. To replace it might cost $70,000 to replace with a new one. I've already replaced the front 4 wheel drive hubs with that objective in mind.

So, as far as getting that 2 to 4% reduction on gas consumption and reduced CO2 emmisions, you can count me out. However, I'm not convinced just going to a xW40 is the right answer for everyone. ( but I am convinced enough to run 5w40 when towing in the summer and the oil cooler is being taxed in the 90 degree weather. ) What I'd like to see is more empirical data on engines that achieved 300,000 miles on their respective viscosity. Also, I need to see this in sophistcated engines with turbos or cylinder deactivation, not grampa's old V-8.

An example is the re-design of Chevy's Gen 5 V-8 in 2014. The 2018 owners manual calls for 0W20 in the Gen V, but still asks for 5w30 in the 6 liter V-8 which is still a Gen 4. It actually says in the manual not to run 30 and 40 weight oils in the 5.3 and 6.2 Gen 5 engines. If someone is running 5w40 in a Gen 5 V-8 since the warranty came off, and they have, 300,000 miles on it without problems, that would be useful. Trouble is, we will have to wait years for that kind of info.

Meanwhile, excellent paper on better gas mileage and reduced CO2 emmisions. Thanks for the post.
 
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Nice read. Thanks for sharing.

I think Dylan may be citing the point that lower viscosity oils result in less friction...

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Originally Posted by wemay
Nice read. Thanks for sharing.

I think Dylan may be citing the point that lower viscosity oils result in less friction...

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Lower friction yes. Less wear I don't know.
 
Originally Posted by Dylan1303
So thin protects better? Thats kinda what i get out of this.



From what I gather,thin lubricants protect better ONLY if the additive pack is stronger to compensate for the lack of thicker oil film protection?
 
Originally Posted by Dylan1303
So thin protects better? Thats kinda what i get out of this.



I think they are talking about lower friction with regards to pumping friction, not lower friction on the surface of the internals. I.E. the oil creates less friction as its pumped throughout the engine passages.
 
what i gather:

-Lower friction with lower viscosity oils is proven.
-Higher viscosity oils have a larger margin for error where wear is concerned.
-Lower viscosity offer "significant fuel consumption benefits..."
-Driver for lower viscosity oils is primarily energy efficiency (govt).

I have a question...

The slide discussing VI (high vs low) states that high VI oils are more efficient at lower temps and less VI oils are more efficient once temps reach 140c. How does this translate to wear, if at all?
 
It seems for thin oil to protect better, the use of MoDTc give better result than ester FM. Time to look into VoA and off the shelf additive ?
 
The way I understand it,hydrodynamic oil lubrication (film thickness) keeps the parts apart. When the oil film is breached the additives kick in,therefore the thinner the oil,the more it depends on the additives to keep the parts from touching,right?
 
Wemay, when comparing a low VI oil to a high VI oil, it still boils down to what is the oil temperature and shear rate in the lubricated parts in question and what is each oil's viscosity at that temperature and shear rate. In the EHL regime, pressure becomes important and viscosity depends also on pressure. Load, speed, area, surface roughness, and other things are important too but they are not a function of the oil. When the viscosity is determined, the problem can be analyzed. It could be that both oils in question provide hydrodynamic lubrication nearly all of the time. If not, then wear becomes a reality. Then the oil that decreases the severity of the contact is at an advantage from the wear standpoint. The effectiveness of the antiwear additives are a factor. They can determine the outcome of which oil allows less wear to some extent, for a given engine part. Some engine parts like bearings are made of soft metals that antiwear additives cannot do much to help. Hard steel on hard steel like many valvetrain parts are very responsive to antiwear additives. The same applies to piston rings against cylinder walls.
 
JAG, revisiting this thread, so antiwear additives work best where hard metals are concerned but overall , boundary thickness is still our number one line protection. I believe Shannow has been impressing this upon me for a while now.

Although i believe in the realworld application of lower viscosity oils performing well enough to protect sufficiently, it is obvious that an HT/HS in the 3.x range offers more protection than one in the 2.x.

As seen in these articles...

https://www.machinerylubrication.com/Read/29185/oil-viscosity-importance

https://www.machinerylubrication.com/Read/30332/viscosity-starved-machines

I wonder if the chemistry science of lower viscosity oils will ever catch up to physical science.
 
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It would be an interesting study to investigate decreasing the viscosity by a large amount and trying different formulations to improve wear rates of all components as best as possible. There might be some problematic parts that the researchers cannot find a formulation that can make survive a long time, relative to how long they do with the manufacturer's recommended viscosity oil.

I have worn out the rings and cylinders of an engine by 200k miles, Due to that and seeing some cars on the road burning enough oil to make smoke, that is the engine area that I am most concerned about. I don't worry about worn out bearings. You may have already seen the paper in the following thread; if not, you may find it interesting: http://www.bobistheoilguy.com/forum...ne-friction-reduction-trends#Post4830433
 
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