Originally Posted by corolla_mike
The 0W oils, as I've come to understand them, are specified for the purpose of raising CAFE standards. The thinner the oil, the easier the engine spins, thereby increasing MPGs.
As we all know, the sturdier the oil, the less the engine will wear.
For the sake of your warranty, do what the mechanical engi... er, uh, socio-political engineers say to do. After that, go with your gut.
The 0 viscosity allows the cold engine to turn over better when it is very cold outside compared to a straight 30 viscosity.
It also allows the oil to circulate and to coat the cylinder walls better until the engine begins to warm up.
Oil viscosity is a science in and of itself.
Think about this for a few.
A straight 30 viscosity will pour out of the can visually like a 30 viscosity at room temperature.
A straight 30 viscosity may very well pour like a 100 weight (Honey) at zero degrees F, when compared to the visual we saw at room temperature.
A straight 30 viscosity may pour like water at 200 degrees F when compared to our visual pouring at room temperature.
A Multi-Viscosity will have a more consistent pour rate at different temperatures. You could say the oil will be more stable.
A Multi Viscosity 0-30 oil may also visually pour like a 30 viscosity at room temperature.
It may look like it pours the same at zero degrees F. (it pours like a straight 0 viscosity oil would if it were now at zero degrees F)
It may visually look like it pours the same at 200 Degrees F. (if you heated a 100 viscosity room temperature oil up to 200 degrees, it would now pour like a 30 viscosity did at room temperature)
In other words, the wider the range, the more stable the visual pour at various temperatures.
It is my understanding that you should not mix different multi-viscosity synthetic oils, because the polymer chains are designed differently for each multi-viscosity product (Synthetics each have very specific polymer chains for each range). Also, in a perfect world, you should not mix different brands of synthetics, because they will use different polymer chains, That is why AMSOIL is Different than Mobil One, They are not the same product.
There really is a difference, the performance between the two will be measurable. We have a lot of decisions. Price, Performance, Convenience. We all have different needs.
This being said, in the long run, you may never see, feel or know the difference. You need oil. Oil needs to flow. Oil needs to coat. Oil needs to flow through the filter. Oil can wear out (Time, Dilution, Blow-by, Moisture and Shear).
The statements above are not based on actual viscosity figures, but instead are just used to illustrate a visual of the reasons for Multi-viscosity.
If you do not follow the points made above, it really is not important. Just follow the Manufactures recommendations.
If you feel 30 will offer your Corolla better protection than a 20 viscosity, it is your Corolla. I will slowly make up my mind as I monitor the break in. Perhaps I may decide on a 0w-30..
Again, the visual Viscosity ratings I applied above are made up.
They do not in any way match up to the actual Industry rating system at the temperatures mentioned above.
Just wanted to give my thoughts; to stress what might not be obvious, that the wider the range of the viscosity, the more stable the pouring rate of oil is at the different operating temperatures.
Did I confuse anyone? Did I confuse everyone?
Visual: Straight 30 at room temperature, Normal
Visual: Straight 100 at room temperature, Honey
Visual: Straight 0 at room temperature, Water
Side Note: the "w" in the spec means Winter.
Some people refer to the W as weight.
The W does not mean weight.
Viscosity has nothing to do with Weight.
It would be wrong to refer to a straight 30 viscosity as 30 weight.
I know that no one here would make that mistake, but it might be useful information for someone... So I included it for free...
Might even add value to my 2 cents worth...