Viscosity Breakdown in Oils

[roaniecowpony]

This applies to all engines, so I thought the "General ..." forum would be the best place to post this.

This video shows testing of various oils and how they breakdown into lower viscosity, with some explanation of why it happens. The takeaway, for me, is that dumping in an oil of xx grade doesn't mean it's that viscosity for most of the oil change interval. So, if you put in a 0w20 or 5w30, it may be a lower grade very quickly.

Take note of the mention of Porsche timing chains as a major cause of shearing/viscosity breakdown. The 3.6 is loaded with many feet of chains, 4 to be specific. The 2.0L has much less, but the chain is still a factor.

Sponsored

 

[TheRaven]

I'd like to also add that the engineers that designed our engines, and those who designed every other modern engine out there, are well aware of this, and draft their oil requirements accordingly.

 

[roaniecowpony]

I'd like to also add that the engineers that designed our engines, and those who designed every other modern engine out there, are well aware of this, and draft their oil requirements accordingly.

Yes. They also have goals that affect their choices for oil selection, that differ from most owners. While they may be willing to sacrifice statistical reductions in engine life for fuel economy, that are economically acceptable to Stellantis, this is likely in opposition to an owner's priority that intends to keep their jeep beyond the warranty.

 

[TheRaven]

While they may be willing to sacrifice statistical reductions in engine life for fuel economy, that are economically acceptable to Stellantis, this is likely in opposition to an owner's priority that intends to keep their jeep beyond the warranty.

Nothing is more economically important to an automaker than drivetrain longevity. So no, they are not going to knowingly "sacrifice statistical reductions in engine life for fuel economy". Especially when we're talking about a significant reduction in engine life for what amounts to statistically insignificant increase in efficiency. They aren't going to knowingly risk having engines blowing up at 80k miles just to get a 0.01mpg increase.

 

[roaniecowpony]

Nothing is more economically important to an automaker than drivetrain longevity. So no, they are not going to knowingly "sacrifice statistical reductions in engine life for fuel economy". Especially when we're talking about a significant reduction in engine life for what amounts to statistically insignificant increase in efficiency. They aren't going to knowingly risk having engines blowing up at 80k miles just to get a 0.01mpg increase.

I'm going to disagree. Profitability of any company is its top priority. Without profitability you don't have a business, you have a philanthropic enterprise.

If a company could magically create an engine or car that would 100% of the time run reliably a specified number of miles, then stop running, they may not do it if it costs too much. They certainly wouldn't have a design goal of lasting as long as possible. That would be economically impracticable. So, they play the game of statistical probabilities of failures and how that affects the bottom line.

Two airplane companies design a plane for the same market. Both had the same target market. But each had slightly different goals. One made their fuselage .062" thick. The other made their fuselage .032" thick. Decades later, it was clear who won the most sales. The thinner one just edged out the thicker one in fuel economy. It was also clear which one lasted longer. The thicker ones lasted much longer than the thinner ones. In the end, the company that made thin airplanes made much more money and beat the other company out of the market completely. Those airliners had original design life around 30,000 hours. But Douglas airplanes were able to continue to fly safely out beyond twice that. The other, not so much, but it burned less fuel. The companies were Douglas and Boeing.

An engine, like an airplane, has a design life. The design life is established by input from marketing, customer support, bean counters, etc. Engineering has a place at the table in the decision, but it isn't their's alone to decide the design life. If it were, many products would last much longer than they do. The project management has to consider regulatory requirements as well as marketing requirements. Engineering has the job of implementing what is possible.

 

[Pape]

Cool about time we get a OIL thread, getting my bad out

This applies to all engines, so I thought the "General ..." forum would be the best place to post this.

This video shows testing of various oils and how they breakdown into lower viscosity, with some explanation of why it happens. The takeaway, for me, is that dumping in an oil of xx grade doesn't mean it's that viscosity for most of the oil change interval. So, if you put in a 0w20 or 5w30, it may be a lower grade very quickly.

Take note of the mention of Porsche timing chains as a major cause of shearing/viscosity breakdown. The 3.6 is loaded with many feet of chains, 4 to be specific. The 2.0L has much less, but the chain is still a factor.

Indeed oil viscosity change during it usage, I lost 0.6 (5.8%) CST (Assumed as start CST is from Manufacturer info sheet) in 3k miles on my last UOA. It did not came from fuel therefore maybe other factor. Unfortunately my data pool is still too small to provide good information.

 

[Old Dogger]

I'm not sure, but I may have posted this before. But it is definitely applicable to the Title of this Thread. The Design Engineer, for the Pentastar 3.6 engine, explains the oil viscosity needed, in certain parts of the engine. In other words, this is from the horses mouth, of the Design Engineer, that designed it. GREAT ADVICE! Please see below:

Nice! As an former Pentastar design engineer I am slightly bias but the engine is really high quality. Few points from the development using tens of millions of dollars in analysis and testing regarding the oil and durability..... The lighter oil was chosen mostly for fuel economy BUT engineering is the science of compromise. You help one thing but hurt another. A thicker oil will reduce timing chain and tensioner wear because the center timing chain idler doesn't go fully hydrodynamic till about 1650rpm on 5w-20. So, a thicker oil will lower that number slightly and with general loads/speeds the engine spends a lot of time around 1500-1750 rpm with the 8 speed. So thicker oil is a win there. Additionally, the earlier engines had what was called the "McDonald's Arches" in the idler bearing which was intended in making a more uniform distribution but in actuality acted as a knife edge. This design was changed around 2014 to a smooth bearing. So overall timing chain issues will likely follow the 2011-2014 engine years more than 2014+. Where you lose.... The head is very complicated with a Type II valve train. Meaning lots of things to pressurize and pump up at start up. A thicker oil didn't do so well here (on long sit times +cold start) and contributed to a overall increased engine wear especially in the head and cam bearings. Last point. This engine needs occasional WOT runs if you want it to last. Granny cycling is bad for it. So bad for it we actually created a new granny cycle test during the cylinder #3 misfire issue. The highest wear is in the valve guides, because of tight valve stem seals (for emissions, reduce oil burn). They basically dry out. When you go WOT/high rpm/load you get some fresh oil in there and this keeps the wear down. Thicker oil might not help this condition but we also change the valves/guides/seals in 2014+. Not sure the impact. Cheers! Kevin PS. Turn off stop start and do not run e85 if you are concerned about engine wear. Eats the engine alive.

 

[NWJeepr]

Other NA V6's from other manufacturers don't seem to share the fate of so many Pentastar top-ends. And they use 20w oils too. Wonder why that is.

The Pentastar used to be spec'd for 5w30 between 2011-late 2012 in JK Wranglers. That was in the thick of when the huge head recalls started.

Maybe the Pentastar is just crap and Stella is remiss in sending it out to pasture, or giving the Jeep a better NA V6 engine design.

Could we also explore the science of oil viscosity in a more meaningful way than clickbaity-sensationalist opinion pieces on Youtube?

 

[Rubenmora1]

so what’s the best oil we should be using in our amazing 3.6 ?

 

[Pape]

so what’s the best oil we should be using in our amazing 3.6 ?

Amsoil man Amsoil

I'm not sure, but I may have posted this before. But it is definitely applicable to the Title of this Thread. The Design Engineer, for the Pentastar 3.6 engine, explains the oil viscosity needed, in certain parts of the engine. In other words, this is from the horses mouth, of the Design Engineer, that designed it. GREAT ADVICE! Please see below:

Nice! As an former Pentastar design engineer I am slightly bias but the engine is really high quality. Few points from the development using tens of millions of dollars in analysis and testing regarding the oil and durability..... The lighter oil was chosen mostly for fuel economy BUT engineering is the science of compromise. You help one thing but hurt another. A thicker oil will reduce timing chain and tensioner wear because the center timing chain idler doesn't go fully hydrodynamic till about 1650rpm on 5w-20. So, a thicker oil will lower that number slightly and with general loads/speeds the engine spends a lot of time around 1500-1750 rpm with the 8 speed. So thicker oil is a win there. Additionally, the earlier engines had what was called the "McDonald's Arches" in the idler bearing which was intended in making a more uniform distribution but in actuality acted as a knife edge. This design was changed around 2014 to a smooth bearing. So overall timing chain issues will likely follow the 2011-2014 engine years more than 2014+. Where you lose.... The head is very complicated with a Type II valve train. Meaning lots of things to pressurize and pump up at start up. A thicker oil didn't do so well here (on long sit times +cold start) and contributed to a overall increased engine wear especially in the head and cam bearings. Last point. This engine needs occasional WOT runs if you want it to last. Granny cycling is bad for it. So bad for it we actually created a new granny cycle test during the cylinder #3 misfire issue. The highest wear is in the valve guides, because of tight valve stem seals (for emissions, reduce oil burn). They basically dry out. When you go WOT/high rpm/load you get some fresh oil in there and this keeps the wear down. Thicker oil might not help this condition but we also change the valves/guides/seals in 2014+. Not sure the impact. Cheers! Kevin PS. Turn off stop start and do not run e85 if you are concerned about engine wear. Eats the engine alive.

Can you define thicker oil ?

 

[TheRaven]

I'm going to disagree. Profitability of any company is its top priority. Without profitability you don't have a business, you have a philanthropic enterprise.

If a company could magically create an engine or car that would 100% of the time run reliably a specified number of miles, then stop running, they may not do it if it costs too much. They certainly wouldn't have a design goal of lasting as long as possible. That would be economically impracticable. So, they play the game of statistical probabilities of failures and how that affects the bottom line.

Two airplane companies design a plane for the same market. Both had the same target market. But each had slightly different goals. One made their fuselage .062" thick. The other made their fuselage .032" thick. Decades later, it was clear who won the most sales. The thinner one just edged out the thicker one in fuel economy. It was also clear which one lasted longer. The thicker ones lasted much longer than the thinner ones. In the end, the company that made thin airplanes made much more money and beat the other company out of the market completely. Those airliners had original design life around 30,000 hours. But Douglas airplanes were able to continue to fly safely out beyond twice that. The other, not so much, but it burned less fuel. The companies were Douglas and Boeing.

An engine, like an airplane, has a design life. The design life is established by input from marketing, customer support, bean counters, etc. Engineering has a place at the table in the decision, but it isn't their's alone to decide the design life. If it were, many products would last much longer than they do. The project management has to consider regulatory requirements as well as marketing requirements. Engineering has the job of implementing what is possible.

Your examples are a lot different than sacrificing drivetrain longevity for a 0.01mpg increase. So yeah, I completely disagree - profitability is directly dependent on their products lasting. The only thing that kills sales worse than a bad reliability reputation is grossly overpriced products.

 

[Old Dogger]

Amsoil man Amsoil



Can you define thicker oil ?

Thicker oil, which means it's more resistant to flow

 

[NWJeepr]

Your examples are a lot different than sacrificing drivetrain longevity for a 0.01mpg increase. So yeah, I completely disagree - profitability is directly dependent on their products lasting. The only thing that kills sales worse than a bad reliability reputation is grossly overpriced products.

Isn't the contention that we once had a 4.0L inline 6 that would march to 400k without complaint, and now we have a finicky V6 that uses aluminum and plastic parts (lighter) and might eek out 200k without needing a top-end rebuild because, lighter weight oils and other marginal improvements in fuel economy - basically a comforting scapegoat, blaming the government for all our problems -

200k is still a good run and doesn't sacrifice reputation, but it's not legendary. What automakers are saying is the bulk of consumers who are the initial buyer don't want to keep a vehicle to 400k anyway, they dump them and buy a new one, probably closer to the 200k mark on a long run. So they feel they can get away with these engineering trade-offs.

 

[Pape]

Thicker oil, which means it's more resistant to flow

So 0w30 would fit your definition of ticker oil ?

 

[Tokenwasp]

Nothing is more economically important to an automaker than drivetrain longevity. So no, they are not going to knowingly "sacrifice statistical reductions in engine life for fuel economy". Especially when we're talking about a significant reduction in engine life for what amounts to statistically insignificant increase in efficiency. They aren't going to knowingly risk having engines blowing up at 80k miles just to get a 0.01mpg increase.

Your examples are a lot different than sacrificing drivetrain longevity for a 0.01mpg increase. So yeah, I completely disagree - profitability is directly dependent on their products lasting. The only thing that kills sales worse than a bad reliability reputation is grossly overpriced products.

Don't really know how anyone could believe this after the last few decades of build quality.

Ask any mechanic - modern cars are built to go 100K miles. After that, all bets are off.

Sponsored