ACEA A3 5-30 vs. not?

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What's in the oil that qualifies one oil eg. 5-30 ACEA A3 and the another just A1? It is simply a thicker viscosity at temp. or is there more of a certain type of additive? eg. BMW Synth. 5-30 is (I believe) A3, but Syntec 5-30 is not, yet both are made by Castrol in NJ. Is it just something they've added "more of" to the oil or a completely different base oil? Or both?
 
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Dr T, ACEA, A3/B4 oils must have a minumum high temp/high shear viscosity of 3.5 centipoise @ 150C. The minimum spec for SAE xw-30 grades is only 2.9 'Cp however. Most xw-30's sold in North America are formulated in the 2.9-3.1 Cp range, in order to help them meet the API "Energy Conserving" designation. If you formulate to meet ACEA A3, it makes it difficult to meet the EC criteria. So most - but not all - of the ACEA A3/B4 oils you find are xw-40 grades. Any 40wt oil is going to have a HT/HS greater than 3.5 Cp, even if it is of poor quality. In addition to this, the standard test matrix for ACEA A3/B4 oils is significantly more difficult to pass. It attempts to analog what the oil would see over the course of an extended drain interval. For example, some of the ACEA test durations are upwards of 250 hours, whereas the API tests are more in the 80-128 hour range. I use ACEA A3/B4 as most of these formulations are also intended for passenger car diesel applications. This requires greater detergency, which is also helpful in long drains. TooSlick
 
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I wanted to add, if you find an xw-30 oil that meets ACEA "A3/B3/B4" specs, it will normally have a viscosity @ 100C in the 11.0-12.5 centistoke range. For example, the Amsoil Series 3000, 5w-30 has a viscosity of 11.4 Cst and a HT/HS of 3.6 Cp @ 150C. Oils in the 9.5-10.5 Cst range will normally be ACEA A1/B1 rated products ....The old Mobil 1, trisyn was ACEA A1/B1 rated for example. So this BMW 5w-30 is probably formulated a bit thicker than your garden variety Syntec and it also would have higher additive levels to help it pass the longer duration ACEA tests. TooSlick
 
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