Euro 5w-30 is fine, but USA 5w-30 is not as thick at 10cSt. HT/HS insufficient for A3.
I called Valvoline a while ago on this. Calling AoA would be a waste of time.
Passat 2.8L V6 eats 5W-30 like it's nothing!
- Thread starter televascular
- Start date
- Status
Euro 5w-30 is fine, but USA 5w-30 is not as thick at 10cSt. HT/HS insufficient for A3.
I called Valvoline a while ago on this. Calling AoA would be a waste of time.
Auto, it really doesn't matter, since the oil companies have "gamed" the HTHS specs by using gobs of VII to increase the high temperature weight. Once the Viscosity index improvers shear chemically or physically, the oil is no longer capable of withstanding such high stresses. It is at about this same point that I believe that people start seeing their engines eat oil. Some of the typical new Audi engines have very low oil consumption until about 2.5 to 3K miles. Suddenly they begin consuming oil at a rate of about 1 qt per 1000 miles. When we went an analyzed a couple of cases with the RS4 engine, we found that fuel dilution had killed the oil.
It's my understanding that the vii's don't add to the HTHS viscosity since they don't hold up under high stress. HTHS is more of an indicator of base oil's viscosity under those harsh conditions.
HTHS is tested only on new oil, not on oil that has been placed under long term driving stress. So, when say a 5W-40 shears to a 5W-25 after 3000 miles of driving and fuel dilution, what do you think that does to HTHS?
"Lubricant Additives: Chemistry and Applications", edited by Leslie R. Rudnick
P310
HTHS viscosity can be adjusted by increasing the viscosity of the base oil or by increasing the viscosity modifier concentration, .... Since the formulation also has to meet kinematic viscosity and cold cranking simulator viscosity limits, there is often only limited flexibility to adjust HTHS viscosity within the bounds of a given set of base oils and additive.
Permanent Shear Stability
The tendencey of an OCP (Olefin CoPolymer) molecule to undergo chain scission when subjected to mechanical forces is dictated by its molecular weight, molecular-weight distribution, ethylene content, and degree of long-chain branching. Mechanical forces that break polymer chains into lower-molecular-weight fragments are elongational in nature, causing the molecule to stretch until it can no longer bear the load. This loss in polymer chain length leads to a permanent degradation of the lubricant viscosity at all temperatures.
Not necessarily every oil is using cost effective OCPs for VII, but there are quite a few oils that seem to have a tendency to shear down by one or one and a half grades.
"Lubricant Additives: Chemistry and Applications", edited by Leslie R. Rudnick
P310
HTHS viscosity can be adjusted by increasing the viscosity of the base oil or by increasing the viscosity modifier concentration, .... Since the formulation also has to meet kinematic viscosity and cold cranking simulator viscosity limits, there is often only limited flexibility to adjust HTHS viscosity within the bounds of a given set of base oils and additive.
Permanent Shear Stability
The tendencey of an OCP (Olefin CoPolymer) molecule to undergo chain scission when subjected to mechanical forces is dictated by its molecular weight, molecular-weight distribution, ethylene content, and degree of long-chain branching. Mechanical forces that break polymer chains into lower-molecular-weight fragments are elongational in nature, causing the molecule to stretch until it can no longer bear the load. This loss in polymer chain length leads to a permanent degradation of the lubricant viscosity at all temperatures.
Not necessarily every oil is using cost effective OCPs for VII, but there are quite a few oils that seem to have a tendency to shear down by one or one and a half grades.
There was a study in the 80's that found that the % decrease in HTHS viscosity is ~1/2 the % change in kinematic viscosity. Things may have changed the 1/2 to some other number in today's oils but it's still probably in the ballpark. I linked it in the Euro oil forum sometime back but am too lazy to find it.
I know it's a test on new oil, but I thought that the test's sole purpose was to shear down the vii's so that the oil's viscosity under sheared conditions would be known before you used it. You were saying vii's are used to increase the hths, where I thought they would not have an impact on the hths viscosity. But, of coarse, I may have been mistaken.
If the VI improver didn't affect the HT/HS viscosity we would see much lower HT/HS numbers on finished PCMOs than we do.
The problem is with VI improvers that are permanently affected by high temp/high shear conditions. Oils that suffer this sort of damage don't recover and the viscosity takes a permanent hit. Thus the goal in formulating is to either (1) use no VI improver at all; or (2) formulate a shear stable VI improver and use it; or (3) use high VI base oils and as little of the less shear stable VI improver as possible.
I see, Thanks G-Man!
- Status
Similar threads
