What viscosity req'd to get A3 ???

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May 28, 2002
I notice that Q.S. Synth's in 5-30, 10-30 and 5-50 are A3 rated (HT/HS >=3.5). They are both 10.5cSt @ 100C whereas M-1 is as follows:

0-30 is 10.3cSt (HT/HS=2.99)
5-30 is 10.0cSt (HT/HS=3.08)
10-30 is 10.0cSt (HT/HS=3.17)

So, at what point in viscosity does an oil become A3 rated?
Dr T,

This is right out of the ACEA 2002 European Oil Sequence for Service-Fill Oils FOr Gasoline Engines

Viscosity Grades "No restriction except as defined by shear stability and HT/HS requirements. Manufacturers may indicate specific viscosity requirements related to ambient temperature."

Viscosity at High Temperature and Shear Rate

"Test Method CEC-L-36-A-97 (Ravenfield)
Properties Viscosity at 150ºC and 10 to
the 6th s to the -1 shear rate
Unit mPa.s
Limits (A3-02) >3.5"

Related Note To qualify for A3 the oil must stay in grade after 30 cycles through a Bosch fuel injector at a temp of 100ºC

[ October 15, 2003, 08:55 PM: Message edited by: pscholte ]
Finally some detail on those ACEA specs.

Got any more?


Originally posted by buster:
I thought it was 3.5> HT/HS.

What I posted is an exact quote from the specs.

By the way, I couldn't re-find the part where it talks about GC being the elixer of life...or something like that!

[ October 15, 2003, 09:17 PM: Message edited by: pscholte ]
Dr T,

It really depends on how shear stable the formulation is, although as a practical matter, it's rare to see an oil with a kinematic viscosity less than 11.0 Cst that will meet the ACEA A3/B3 specifications.

So what does this say about M-1 30 weight lubes? That they are just slightly thinner at 100C than other 30 weights, but shear down and can't qualify for A3 (150C at 1 hr., etc.)?
HT/HS does not prove how shear stable an oil is. Mobil 1 0w-40 has a HT/HS of 3.6, M1 10w-30 of 3.2. Which one shears? The 0w-40. There have ZERO cases of M1 5w/10w-30 oils shearing down at all. In fact, I believe they are more shear stable then oils with the A3 rating such as Amsoil. There is a 17k mile M1 report where the oil was still in grade after 17k miles!! Specs are not everything and in this case it shows that Mobil 1 is a very high quality lubricant bc it holds it's grade as good as any oil out there and that is a fact based on every UOA on this website. Have a look for your self.
I printed a copy of the Quaker State tech data sheet and I noticed the statement under features: European ACEA A3-98/B3-98 engine test protection standards (5W-30 & 10W-30). I think that what that statement really means is that the oil does not meet the out of date 1998 ACEA A3-98/B3-98 standards but should protect an engine as well. Perhaps any lawyers out there can comment on the wording of that statement from Quaker State. The specs for the 5W-50 state: European ACEA A3-98/B3-98 (5W-50). That appears to me to say that the 5W-50 viscosity really is certified as ACEA A3-98/B3-98.

The Castrol Syntec and Mobil 1 lines of synthetic oil look much better as all grades are certified to meet either the ACEA A5/B5 or A3/B3/B4 or some combination of those specs. ACEA A5/B5 and A3/B3/B4 are extended service stay in grade motor oils and are much better that any A1/B1 and A2/B2 oils that I would imagine are comparable to the API Sl/CF. Castrol just recently updated the specifications for the 0W-30, 5W-30, and 10W-30 viscosities.

I think the tech data for the Quaker State 5W-50 does not look as good as the data for the Castrol Syntec 5W-50. I had been planning on doing a UOA on Castrol Syntec 5W-50 but unfortunately I started having transmission problems with my "beater" 1994 Geo Prizm so I just donated that car to charity. I have only seen three UOA's on Syntec 5W-50 but all looked very good including the one that was on a BMW F650 motorcycle.

[ October 16, 2003, 05:30 PM: Message edited by: Sin City ]
I agree I was confused too re: the 2 lines of A3...however, can you post the link to the updated Castrol Syntec product data sheet?

What from the data would suggest that the Q.S. 5-50 doesn't look as good as Syntec? The pour point is within 2 degrees as it seems to be slightly thicker (18.2 vs. 17.5) than the Syntec.
Dr. T, I just contacted Castrol and asked for a new tech data sheet for the 0W-30, 5W-30, and 10W-30 Syntec. If they send me a new tech data sheet I will forward you a copy of the PDF file. In the past Castrol has had all grades of Syntec on one sheet (0W-30 through 20W-50).

Now that you mention it the Castrol Syntec 5W-50 and Quaker State Full Synthetic Motor Oil 5W-50 do look very similar. The higher flash point and lower pour point of the Syntec is still so close to the numbers for the Quaker State synthetic oil that in the real world the difference probably means nothing. I think it is unlikely that the Quaker State synthetic oil has a very high amount of PAO or Ester since it does not have a very low pour point. The very high viscosity index of 193 for the Qaker State synthetic oil would seem to indicate to me that it may not be as shear stable as the Syntec or for that mater most other synthetic motor oils avilable. The V.I. of Castrol Syntec 5W-50 is 175 and the V.I. of Mobil 1 0W-40 is 187 and many people have critisized these oils for not being shear stable. Still both Castrol Syntec 5W-50 and Mobil 1 0W-40 have both given good wear numbers. I have never seen any UOA's on Quaker State synthetic oils so I can only speculate as to how good they may be.

[ October 17, 2003, 12:02 AM: Message edited by: Sin City ]
Shear stability when done in a bench test, and stay-in-grade capability during service life is two different matters when qualifing an engine oil.
An engine oil can be blended to stay in grade by balancing the thickening due to oxidizing, contaminant load, and boil-off, and thinning due to the shearing of the base oil.
The Bosche test does not take into account the time and service life of the engine oil.
The test only determines the shear stability of the blend, and not the other factors and tests that qualify an A-3 engine oil.
Sonic shearing is another methiod of determing the quality of a base oil.

Shear stability when done in a bench test, and stay-in-grade capability during service life is two different matters when qualifing an engine oil.

Yes, I should have said stay-in-grade capability during service life. Thanks for the correction.
The ability of an engine oil to stay "in-grade" during its service life can be attributed to the blender's skill, judgement, and educated quess work as well as the quality of the ingredents.
I know that the above comes off sounding like a statment by an expert, but it is not, and I am not.
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