Originally Posted By: windeye
I started reading the article by Dr Haas in the Motor Oil University section, not yet finished. In describing the formulation difference of mineral multigrade oil and synthetic multigrade oil, he stated that mineral 10W-30 (example of multi-grade) uses straight 10 oil and then VII to make it thicker to meet 100C viscosity, while as synthetic 10W-30 oil uses straight 30 oil and no VII's. Is this correct? Then how does synthetic 10W-30 meet 10W requirement? Excerpt as follows:
Quote:
A 10W-30 multi-grade mineral based oil is made from a 10 grade oil and has VI improvers added to thicken the product in a 212°F engine. It acts as a 30 grade oil when hot. It acts more as a 10 grade oil at startup. I remind you that a 10, 5 or 2 grade oil is still too thick to provide lubrication at startup. They are all too thick at startup. There is currently no engine oil thin enough to operate correctly at startup. They all cause excessive wear at startup. Again, we are discussing the needs of my single hypothetical engine for around town driving.
Oil Type Thickness at 75° F Thickness at 212° F
Straight 30 250 10
10W-30 100 10
0W-30 40 10
Straight 10 30 6
Straight 5 20 4
Straight 2 15 3
Straight 0 12 3 ( est )
( Oil Types – Synthetic / Straight varying Thickness )
Let’s look at the make up of synthetic based oils. A 10W-30 synthetic oil is based on a 30 grade oil. This is unlike the counterpart mineral oil based on a 10 grade oil. There is no VI improver needed. The oil is already correct for the normal operating temperature of 212°F. It has a thickness of 10 while you drive to work. It will never thin yet has the same long term problem as the mineral based oil. They both thicken with extended age.
That statement by Dr Haas is not correct. There is no fundamental difference between the formulation of conventional oils and synthetic oils. Without viscosity-index improvers, they would both be thinner at 100 C than with viscosity-index improvers.
However, it's true that synthetic oils have lower concentration of viscosity-index improvers because the base-oil viscosity indexes are higher. Therefore, if the base oil used in a conventional 5W-30 oil has a 4 cSt (@ 100 C) viscosity, the base oil used in a synthetic 5W-30 oil may have a 6 cSt viscosity. (The resulting 5W-30 oil has about 10 cSt viscosity.) That's because the concentration of viscosity-index improvers is less in the synthetic oil, as the base oil has a higher viscosity index. Base oils can be chosen such that the concentration of viscosity-index improvers can be under 3% for a synthetic 0W-20 or 5W-30. This will result in very little permanent oil shear (viscosity loss) and help reduce oil deposits greatly. Nevertheless, note that many synthetic oils sold out there have a lot of viscosity-index improvers in them -- usually less than in conventional oils but still a lot more than 3%.
That article makes some very good points. I especially like the discussion of oil pressure and oil flow. However, it makes some serious false statements regarding basic lubrication as well. One would be the one above. Here is another one:
"As it turns out synthetic oils do cling to parts better as they have higher film strength than mineral oils. Synthetics are thinner overall. They have greater slipperiness. Yet they stick better to engine parts. Again, this concept is the opposite of normal thinking."
This paragraph makes so many blatantly false statements at once that it's almost ridiculous. Most synthetic base oils (except for esters) have poor lubricity and solubility and they don't cling to metal parts -- they are dry oils. (Esters have their own problems -- they block the AW/EP/FM additives and increase wear if used alone.) Synthetics are not thinner in general -- they come in any viscosity. It's true that they have less surface friction. However, they don't stick well to the engine parts -- they have low lubricity. They don't have higher oil-film strength. On the contrary, they have lower oil-film strength due to lower pressure - viscosity coefficients as well as lower lubricity.
