The base oil for dino vs. synthetic

[db500]

I was reading a link at ferrarichat http://ferrarichat.com/forum/faq.php?faq=haas_articles#faq_motor_oil_basics where the (apparently) knowledgeable author suggested that dino oil is a thinner base (10W for a 10WXX oil) with VII's to get it to the desired higher weight at operating temp (30W or 40W for example), whereas synthetic oil is made of a thicker base (40W for a XW40)with additives to give the thinner weight at low temps (the OW or 5W).

First time I've heard this...it is true that synth oils don't use VII's? If that is the case, why do synth oils like Mobil1 0W40 reportedly sheer down to 0W30 fairly quickly?

 

[d00df00d]

AFAIK:

There is no hard-and-fast rule. You can add VI improvers to keep an oil from thinning out at high temps, you can add pour point depressants to keep the oil pumpable at low temps, you can use a base stock that has the right viscometrics on its own and doesn't need the help, or you can do any combination of the above. Any given combination will have its own advantages and disadvantages, so which one is best depends on the goals of the formulation. This goes for dinos and synthetics, the only difference being that synthetics generally don't need as much help to get good numbers.

Keep in mind that not all VIIs are polymers. Esters and PAOs, for example, can do the job. Thus, you could have a substance that is playing multiple roles, acting as a VII while it also improves the oil in some other way.

When you see a multi-grade oil with a really broad viscosity spec, like 0w-40, that is usually a thin oil + VII combination. That's why some of them tend to shear and many of them have relatively low HTHS viscosities.

Again, this is AFAIK. Hopefully someone more knowledgeable can chime in.

 

[LargeCarManX2]

[First time I've heard this...it is true that synth oils don't use VII's? If that is the case, why do synth oils like Mobil1 0W40 reportedly sheer down to 0W30 fairly quickly? [/quote]

Straight weights don't use viscosity improvers! Both synthetic and mineral oil use carrier oils of group I flavor I believe! Shearing is a design factor that most the time is corrected by the blender after testing in the real world.

 

[MolaKule]

Actually, both base oils start off with approx. a viscosity of base oil that measures a kinematic viscosity of 5.0 cSt at 100 degrees celcius, so they are both the same viscosity or thickness at that temperature.

The greater the Viscosity Index (VI) number of the base oil mixture, the better it performs over wide temperature ranges.

The difference between the two is the Viscosity Index or VI. A mineral oil has a lower VI which means that it will thicken up sooner at lower temps, and thin out sooner at higher temps, whereas synthetic oils are just the opposite; that is, synthetics hold their viscosity values over widely varying temperatures.

Most base oils (mineral and synthetic) are a binary (two base oil viscosities) or ternary (three) or more mixtures of different viscosities. For a binary mixture you take the 5.0 cSt oil and mix it with a thicker oil. For a ternary mixture, you take three base oils, etc.

The thinner base oil helps the oil to flow better at low temps and get better pour points, while the thicker (higher viscosity) base oil helps to keep the oil from thinning at high temps; the thicker base oil also reduces volatility, and increases shear resistance, as d00df00d has stated.

In minerals oils, to get a higher VI number, more viscosity index improver (VII) is added to compensate for the low natural VI of the base oil.

In synthetic oils, little or no VII polymer is added since synthetic oils have a higher VI with which to start.

Generally speaking, for multi-viscosity oils (X W XX), the greater the difference in the low-temp, high-temp number, more VII's are added to span the viscosity or weight range.

Today, better VII's have been developed which shear much less than the VII's of yonder years. Many VII's have Shear Stability Indices of 25-38, which is remarkable. In addition, many can reform their molecules after shearing takes place.

So it's not as simple as that person suggested.

 

[DieselTech]

Originally Posted By: MolaKule
Actually, both base oils start off with approx. a viscosity of base oil that measures a kinematic viscosity of 5.0 cSt at 100 degrees celcius, so they are both the same viscosity or thickness at that temperature.

The greater the Viscosity Index (VI) number of the base oil mixture, the better it performs over wide temperature ranges.

The difference between the two is the Viscosity Index or VI. A mineral oil has a lower VI which means that it will thicken up sooner at lower temps, and thin out sooner at higher temps, whereas synthetic oils are just the opposite; that is, synthetics hold their viscosity values over widely varying temperatures.

Most base oils (mineral and synthetic) are a binary (two base oil viscosities) or ternary (three) or more mixtures of different viscosities. For a binary mixture you take the 5.0 cSt oil and mix it with a thicker oil. For a ternary mixture, you take three base oils, etc.

The thinner base oil helps the oil to flow better at low temps and get better pour points, while the thicker (higher viscosity) base oil helps to keep the oil from thinning at high temps; the thicker base oil also reduces volatility, and increases shear resistance, as d00df00d has stated.

In minerals oils, to get a higher VI number, more viscosity index improver (VII) is added to compensate for the low natural VI of the base oil.

In synthetic oils, little or no VII polymer is added since synthetic oils have a higher VI with which to start.

Generally speaking, for multi-viscosity oils (X W XX), the greater the difference in the low-temp, high-temp number, more VII's are added to span the viscosity or weight range.

Today, better VII's have been developed which shear much less than the VII's of yonder years. Many VII's have Shear Stability Indices of 25-38, which is remarkable. In addition, many can reform their molecules after shearing takes place.

So it's not as simple as that person suggested.


Um yeah what he said

 

[Johnny]

This is one of those post that should be sticked somewhere on this site.

Thanks MolaKule