Question on weight ratios and VII

[MrCPU]

Somebody posted a link about "All about oil", and it was a good read, and I learned much. However, I have a question.

A mention was made in the paper about the amount of VII's needed to make a multi-grade oil, and that a 5w30 oil (with a ratio of 6), required more VII's than a 10w40, which would only be a ratio of 4. a 15w40 about 2.5, etc....

If this is true, and the VII's are the things that are breaking down, then all other things being equal, and temperature not an issue, using a 10w30 would be better, or last longer, than a 5w30, given less need for VII's. Fewer of them to break down, less total reduction in viscosity over the life of the oil.

Am I even close?

 

[addyguy]

At a basic level, yes, you have it right. But VII 'breakdown' isn't as much of an issue these days as it was in years past - the broken down VII's don't cause problems (sludge) like they used to. 5w30's are generally well-regarded b/c they offer better cold-start flow and lubrication. However, above about 0 Farenheight, this isn't really an issue....

 

[glenncof]

No expert here but...generally you are right if the base oils have the same VI to start with.

Some base oils have better VI without VII's. These would require less VII for the same range.

http://www.chevron.com/products/sitelets/baseoils/docs/ebot.pdf

Above is a good treatment on the topic.

 

[FrankN4]

With the "ALL ELSE EQUAL" A 5w30 will shear more than a 10w30.
However, the 5w30 usually starts out with a higher 100C cSt than a 10w30 so it has more "ROOM" to shear. A typical non high mileage 10w30 will start out with a 100C cSt of 10 up to about 10.7 with 10 to 10.2 about average. A typical 5w30 will start out with a 100C cSt of 11 to 11.3. At around 6000 miles they are about equal if you go that long on OCI. One advantage to the 5w30 is that it will have a little better high temperature cSt over the useful life of the oil.

Also, remove the "ALL ELSE EQUAL" and you do have some base stock and addative packages that shear more than others.

What I do not know is the downside to the shearing of the VII polymers. I do not know if there is any problem such as residue, sludge, or what.

 

[coffee]

Well, if I am changing my oil 5-7k OCI's then a 5w30 would probably be better overall then the 10w30? I am about to buy dino oil for my Volvos and will get the Havoline brand and after what you stated it appears that 5w30 may be better for my 5-6k OCI's.

 

[jorton]

Originally Posted By: glenncof
No expert here but...generally you are right if the base oils have the same VI to start with.

Some base oils have better VI without VII's. These would require less VII for the same range.

http://www.chevron.com/products/sitelets/baseoils/docs/ebot.pdf

Above is a good treatment on the topic.



Don't have time to load the 12 pg pdf with dial-up.

Do you think 5w and 10w use the same base oil mixtures, or is the idea 5w uses a better class than 10w just hearsay?