A discussion about VIIs

[BigTimeTA]

Yesterday, I was talking with a mechanic and he said that VIIs do not upscale neither hydrodynamic protection nor film strength. VIIs Just slow down the flow at operating temperature. I was just wondering if he's telling me a fact rather than an opinion.
This discussion was interesting because I thought that VIIs scales film strength from a lighter base viscosity.

I was also wondering if there are types of VIIs that could upscale film strength, like there are some types that are shear stable.

 

[BMWTurboDzl]

Yesterday, I was talking with a mechanic and he said that VIIs do not upscale neither hydrodynamic protection nor film strength. VIIs Just slow down the flow at operating temperature. I was just wondering if he's telling me a fact rather than an opinion.
This discussion was interesting because I thought that VIIs scales film strength from a lighter base viscosity.

I was also wondering if there are types of VIIs that could upscale film strength, like there are some types that are shear stable.

He's correct.

A Simple Explanation of Viscosity Index Improvers

Viscosity index, noun An arbitrary scale for lubricating oils that indicates the extent of variation in viscosity with variation of temperature. Improver, noun A person or thing that...

www.machinerylubrication.com

"..
Viscosity modifiers are polymeric molecules that are sensitive to temperature. At low temperatures, the molecule chain contracts and does not impact the fluid viscosity. At high temperatures, the chain relaxes and an increase in viscosity occurs.

There are two ways to explain the characteristics of these polymer chains. The first is to compare the polymers to people. When a person is cold, his natural reaction is to hold his arms close to his body to retain warmth. Now imagine a crowd of cold people, arms drawn in, moving past one another in a congested hallway. Sure there is some congestion, but the people can still move freely.

Now imagine the opposite. When a person is hot, he tends to sprawl out. Picture a person holding his arms straight out from his sides. It would be much more difficult to navigate a congested hallway full of hot people, arms extended. Consider in this example, the flow of people is related to the viscosity of the crowd.

Another way to describe this chain is in comparison to a slinky, a lazy-spring coil-shaped toy.1 Working in a way similar to the people in a hallway analogy, the slinky contracts when cold and stretches out when hot. When contracted, the molecules flow past one another easily, but when extended, they get caught on one another and impede the flow of the fluid they occupy.

Keep in mind that as temperature increases, the viscosity decreases. The addition of modifiers will only slow down the rate at which the viscosity decreases.
..."

 

[zfasts03]

So basically, don't use a 0w winter rating unless you are in a climate where it is needed?
...or maybe if trying to get the most mpg?
...or lots of short trips where the oil is spending lots of time below operating temperature?

 

[kschachn]

So basically, don't use a 0w winter rating unless you are in a climate where it is needed?
...or maybe if trying to get the most mpg?
...or lots of short trips where the oil is spending lots of time below operating temperature?

In order to obtain a 0W winter rating sometimes a better base stock is used that requires less VII. So it’s not an absolute. Plus not all VII are the same, there are some that are more shear and oxidatively stable than others.

 

[BMWTurboDzl]

So basically, don't use a 0w winter rating unless you are in a climate where it is needed?
...or maybe if trying to get the most mpg?
...or lots of short trips where the oil is spending lots of time below operating temperature?

The winter rating is largely irrelevant with regards to the operational viscosity. For example M1 and Castrol and others offer excellent 0w40 that outperforms a majority of 10w30s.

 

[kschachn]

Plus the difference in winter ratings is only significant at very low to low temperatures. An engine that spends "lots of time below operating temperature" is still going to be way above where the winter rating makes any sort of difference.

 

[Bill_W]

VII’s are known to improve MPG. Not really important to anyone here but some car manufacturers oils use them along with thinner base oils. In SoCal maybe 5w-20 would give more durability than a 0w. (IMO)

 

[PimTac]

VII’s are known to improve MPG. Not really important to anyone here but some car manufacturers oils use them along with thinner base oils. In SoCal maybe 5w-20 would give more durability than a 0w. (IMO)

Maybe not.

 

[KrisZ]

Yesterday, I was talking with a mechanic and he said that VIIs do not upscale neither hydrodynamic protection nor film strength. VIIs Just slow down the flow at operating temperature. I was just wondering if he's telling me a fact rather than an opinion.
This discussion was interesting because I thought that VIIs scales film strength from a lighter base viscosity.

I was also wondering if there are types of VIIs that could upscale film strength, like there are some types that are shear stable.

That is not true, flow stays pretty much constant throughout the temperature range. Flow changes with pump RPM, nothing else affects it in any meaningful way.

VII slow down the change in viscosity as the temperature increases. Hence the term “multi grade” oil.

 

[Link]

Is Mobil 0w40 fs loaded with the unwanted VII’s?

 

[kschachn]

Is Mobil 0w40 fs loaded with the unwanted VII’s?

Mobil 1 0W-40 is one of the best oils on the market with many demanding approvals. Same goes for Castrol 0W-40.

 

[Accent Abuser]

So basically, don't use a 0w winter rating unless you are in a climate where it is needed?
...or maybe if trying to get the most mpg?
...or lots of short trips where the oil is spending lots of time below operating temperature?

That's why HTHS is important, although I remember reading on here gokhan had a pretty solid theory on base oil viscosity having an impact on extreme shear/temperature performance like conditions seen by the valve train and timing chain. Me, I tend to stick to 10w/15w in summer for that reason, it might make a difference, and it certainly won't hurt in higher temps. If you're someone who only changes oil once a year and live in a cold climate than it probably won't be possible to use a higher winter rating.

 

[SteveG4]

That's why HTHS is important, although I remember reading on here gokhan had a pretty solid theory on base oil viscosity having an impact on extreme shear/temperature performance like conditions seen by the valve train and timing chain. Me, I tend to stick to 10w/15w in summer for that reason, it might make a difference, and it certainly won't hurt in higher temps. If you're someone who only changes oil once a year and live in a cold climate than it probably won't be possible to use a higher winter rating.

This could be a thread all by itself. Probably was, perhaps more than one, if I recall correctly.