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... viscosity is less important than HTHS & resistance to oxidation & shearing. Now that I've done the comparison, I think Saab's documentation also trends this way. I'll admit, that's NOT what I thought before I did the comparison. Since all of the 12 oils currently meeting GM-LL-A-025 are full syn, they should have excellent resistance to both oxidation (thickening) & shearing (thinning). Since 7 of them are also A3 rated, they provide better bearing protection than the other 5. I don't think it matters that 6 of those 7 A3 rated oils are 0W-30s, as long as they maintain those other "critical to protection & longevity" properties. This is why I didn't list a viscosity in the "Conclusion." I wouldn't hesitate to run M1's 0W-30 if it had the same A3 rating it does in Europe. But since the only choice in the US for both ratings on the same oil is the M1 0W-40, I'd choose that one every time for my vehicle. Without seeing the GM-LL spec, I'd guess that fuel economy is a dominant factor in it. (This is hinted at in the '03 9-3SS owner's manual, which says the GM-LL oil offers both high standards & fuel efficiency.) Since M1 0W-40 meets GF-3 specs for fuel economy (there are no economy goals for A3), I'm positive that's why it's on the GM-LL list. The M1 15W-50 in my 900 has started just as quickly down to 15*F as the 10W-30 Syntec I was running before it, but I'm sure it's not fuel-efficient enough to ever get GM-LL approval.
I do agree that current measures used to gauge oil changes are only convenient SWAG's. No, you can't go strictly by someone else's experience, but there's enough evidence compiled by others to indicate that ANY Group IV syn should hold up for 10k miles in a turbo. If you make it A3 rated, then you should also get the bearing protection for that interval. The OLM, since it doesn't test the oil, is still a SWAG, but has more S & less WAG than the other methods.
Then there's the INconvenience of oil analysis. Sure, it's the most accurate way to determine you oil's condition, but it's such a hassle for someone with just a couple of cars (as opposed to a business with a fleet of vehicles). For the business fleet, it's stupid if you DON'T analyze the oil, since the potential damage costs & wasted oil costs can get so high. But for John Q. Public, who can't be bothered with the cost & inconvenience of oil sampling when Jiffy Lubes are on all the corners that Starbucks' aren't, it's a wacko procedure. Since I'm so wrapped up in this right now, I'll be testing the oil in both cars at 10k miles out of sheer curiosity. The reason I decided to also test the 0W-40 in my 9-3 at 5k is because it'll be approaching the end of its warranty. I don't fear for the condition of the oil, but I do for the head gasket, & this is the easiest way to document its condition. Once I'm OOW, I'll probably get it analyzed just once or twice more to get a good comparison of how we drive the car over several years' time. After that, I'm sure I'll be obsessed with something else.
posted by 216.160.177...
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