Another revisit about Viscosity Index and VII...

[widman]

To point #1, once you get the engine warm, you want to maintain viscosity, and the difference between one part and another of an engine is not significant viscosity wise.
To point #2, that's not exactly what was said. The dino has VI improvers to keep it from thinning out too much at high temps (and flow improvers for low temps). The Synth has flow point improvers (or simply different synthetics to flow better).
so once a dino shears out, or loses it's polymers, it is a thin oil. If a synth lost it's flow improvers (don't think that can happen) it would still be the thicker oil.

 

[The_Oz]

Alright,

Here's a bunch more questions for you guys.

1) I've read that a high Viscosity Index is best in choosing a motor oil. Now, I've also read that VI is an indication of how quickly the oil changes its viscosity depending on the temperature that it encounters. Having said that, different parts of the engine experience different operation temperatures. The oil also experiences different shearing stresses in different locations within the motor. If a high VI means that the oil will change its viscosity flow slower than an oil with a low VI, wouldn't that be a bad thing?

2) Now, Bob, MolaKule, and others stated that "normally" dino-based oils are made using thin weight oils, and then mixed with VIIs so that it can flow thicker at 100C. And synth. based oils are formulated thicker, and then mixed with VIIs to flow thinner at 40C. Now, if - for any reason - the VIIs breakdown, would a dino-based oil still flow thick at 100C? Would a synth.-based oil flow at 40C?

Comments?

Oz

 

[The_Oz]

quote:

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Originally posted by widman:
To point #2, that's not exactly what was said. The dino has VI improvers to keep it from thinning out too much at high temps (and flow improvers for low temps). The Synth has flow point improvers (or simply different synthetics to flow better).
so once a dino shears out, or loses it's polymers, it is a thin oil. If a synth lost it's flow improvers (don't think that can happen) it would still be the thicker oil.

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Widman,

That's not what I gather from this discussion.

http://theoildrop.server101.com/ubb/ultimatebb.php?ubb=get_topic;f=1;t=000438#000001

But I think you confirmed my suspicions though. Once VIIs breakdown in dino oils, it will flow too thin (ie. 5W30 will flow like 5wt).

Regards,

Oz