Originally Posted By: JAG
Most OTC 5W-30 synthetics still have more polymeric VIIs than their 10W-30 counterparts but the difference is not very big. I believe the best choice depends on the situation: engine, driving habits, climate, etc.
In theory a typical GP III 10W-30 syn' may be slightly more shear stable than it's 5W-30 counterpart but the trade off is usually a massively lower VI which to my way of thinking simply isn't worth it. If you need a heavier 30wt oil choose a heavier 5W-30 or even 0W-30 oil with a higher HTHSV rating and leave the 10W-30 syn on the shelf. This way you won't be significantly raising the start-up viscosity (even in the summer) of the oil you're using which is what happens with every 10W-30 syn'.
There has been a lot of progress in the past 10 years or so in motor oil quality, specifically with regard to VIIs. This has allowed for a steady increase in the viscosity indexes of motor oil. The 10W-30 oil grade with it's typical 140 range VI is yesterdays oil grade; for all intend and purposes it is obsolete. For example M1 10W-30, a very light 30wt oil with it's HTHSV of 3.0cP is heavier than M1 0W-40 and PU 5W-40 on start-up at temp's as high as 50F.
The two main reasons the 10W-30 grade still exists is because it's cheaper to make than a 5W-30 (higher margin) although it rarely ever sells at a discount to the 5W-30 grade, and people continue to buy it largely out of ignorance.
Most OTC 5W-30 synthetics still have more polymeric VIIs than their 10W-30 counterparts but the difference is not very big. I believe the best choice depends on the situation: engine, driving habits, climate, etc.
In theory a typical GP III 10W-30 syn' may be slightly more shear stable than it's 5W-30 counterpart but the trade off is usually a massively lower VI which to my way of thinking simply isn't worth it. If you need a heavier 30wt oil choose a heavier 5W-30 or even 0W-30 oil with a higher HTHSV rating and leave the 10W-30 syn on the shelf. This way you won't be significantly raising the start-up viscosity (even in the summer) of the oil you're using which is what happens with every 10W-30 syn'.
There has been a lot of progress in the past 10 years or so in motor oil quality, specifically with regard to VIIs. This has allowed for a steady increase in the viscosity indexes of motor oil. The 10W-30 oil grade with it's typical 140 range VI is yesterdays oil grade; for all intend and purposes it is obsolete. For example M1 10W-30, a very light 30wt oil with it's HTHSV of 3.0cP is heavier than M1 0W-40 and PU 5W-40 on start-up at temp's as high as 50F.
The two main reasons the 10W-30 grade still exists is because it's cheaper to make than a 5W-30 (higher margin) although it rarely ever sells at a discount to the 5W-30 grade, and people continue to buy it largely out of ignorance.
