Synthetics and VI

[mechanicx]

I'm not real versed in oils and that's why I'm here. I've heard that synthetics don't have and don't need viscosity index improvers (VII) as dino oils do. This seems good to me because VII are not really lubricants and they can shear down.

My question is if synthetics don't have VII then how can a synthetic be 5W30 or 0w30? Or for that matter how can you have 0W30 and 0W40, or 5W20 and 5W20..I think you get the idea? I'm sure I'm missing something, but my understanding was that a 5W30 would have a slightly higher actual weight at 32F than a 5W20 does, but still be within a certain range to be a 5W rating. So how can you have so many viscosities without VII? I'm going to assume they blend different weights of synthetics together, but that doesn't sound good.

 

[Pablo]

Synthetic lubricants have a naturally higher viscosity index.

Some synthetics do use VII's.

 

[DieselTech]

Does anyone know if PP has VII's?

 

[Johnny]

Yes it does.

 

[DieselTech]

I knew you wouldn't be far behind on that question. Thanks Johnny!!

 

[d00df00d]

Originally Posted By: mechanicx
My question is if synthetics don't have VII then how can a synthetic be 5W30 or 0w30? Or for that matter how can you have 0W30 and 0W40, or 5W20 and 5W20..I think you get the idea? I'm sure I'm missing something, but my understanding was that a 5W30 would have a slightly higher actual weight at 32F than a 5W20 does, but still be within a certain range to be a 5W rating. So how can you have so many viscosities without VII? I'm going to assume they blend different weights of synthetics together, but that doesn't sound good.

Remember, VII means viscosity index improver. A synthetic will have a better viscosity index to start with, so it won't need as much improvement. For some grades (e.g. 5w30), it won't need any improvement at all. It just naturally resists thickening and thinning well enough on its own to make that grade, so it doesn't need anything added to it.

Sometimes an oil with a broad viscosity rating (e.g. 0w-40) will still have VIIs, but usually not much if it's a good synthetic.

 

[mechanicx]

OK thanks for the info. I always assumed that synthetics had at least some VII just as conventiol multi-grade does.I got the idea that synthetics didn't have VII from I think some Dr. Haas article, but maybe I skimmed through it too fast.

So a synth. 5W20 would have the lowest maybe zero VII

? Is this why 0Wxx isn't always recommended by automakers but 5Wxx instead?


Can anyone break down for me the meaning and application of an oil's viscosity index as relates to oil wieghts, VII etc.?

 

[Doug Hillary]

Hi,
mechanicx - Not all VIIs are single purpose components in the formulation of synthetic lubricants. Some are multi purpose especially where phosphoric acid is part of the formulation (common)and they may act as dispersants, anti oxidants and etc

VIIs are an enhancement to the base and todays "modern" versions are quite shear stabile

 

[mechanicx]

Originally Posted By: Doug Hillary
Hi,
mechanicx - Not all VIIs are single purpose components in the formulation of synthetic lubricants. Some are multi purpose especially where phosphoric acid is part of the formulation (common)and they may act as dispersants, anti oxidants and etc

VIIs are an enhancement to the base and todays "modern" versions are quite shear stabile


I knew this was going to get complicated. It still seems like it would be best to have less VIIs and use other additives for other needed properties, but I guess it's not so clear cut.

Is it gernerally true that 5W20 has a lower viscosity at say 32F than 0W30?

 

[sangyup81]

I would put my money on the 0W30 at 32F being thinner than a 5W20 but there are variances among different brands of oil.

 

[Tom NJ]

Most synthetic multi-grade oils contain VI Improvers, just usually less. Even those that claim they do not use VIIs use other multi-functional polymeric additives such as dispersants, high viscosity PAO, PPDs, etc. that serve partially as VIIs.

Most synthetic base oils have a natural VI of 120-140, while the finished multi-grade oils have VIs of 150-190.

Tom NJ

 

[d00df00d]

Originally Posted By: mechanicx
So a synth. 5W20 would have the lowest maybe zero VII

? Is this why 0Wxx isn't always recommended by automakers but 5Wxx instead?

AFAIK, a 0w-20 has to be fully synthetic, but a 5w-20 doesn't. Manufacturers usually prefer not to specify a synthetic unless they have to, so I would imagine that if they want a 20-weight oil, it is more likely to be 5w-20 so that it doesn't have to be synthetic.


Originally Posted By: mechanicx
Can anyone break down for me the meaning and application of an oil's viscosity index as relates to oil wieghts, VII etc.?

All oils thicken when cold, and thin out when hot.

The higher the viscosity index, the less it thickens when cold or thins out when hot. In other words, its viscosity changes less as the temperature changes.

When you look at a viscosity grade, like 5w30, a bigger difference between the two numbers usually indicates a higher viscosity index.