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I don't know who you're talking to about motor oil, but they sure don't know how multi-grade viscosities work. (In all fairness, I haven't met ANY mechanics who do! For mechanical things they're great, but for fluid dynamics they need more study time.)
Let's take 10W-30 as an example. The rating only means that the oil flows like a frozen 10 wt when it's really cold (0°F) instead of a frozen 30 wt (which would be thicker than you'd like at 0°F) & then behaves like any 30 wt would when it's hot. The cold rating (xW- end of things) should be viewed as being completely separate from the hot rating (the 30, 40 or 50 wt part) & is simply a labeling convenience to help you pick an effective oil for your start-up climate. The hot rating is where you'll get all your operating temp protection, & should be chosen based on the engine's design & protection needs. Separate them in your mind!
Done that? OK, good! Now consider this: ANY motor oil will be thicker below 100°F than ANY OTHER motor oil will be above 210°F!! What does THAT really mean? It means the "thinnest" 0W-20 will be thicker for all of your cold starts in Pasadena than the "thickest" 15W-50 will be once the engine's warmed up to operating temperature!
5W-30 & 10W-30 are both "thinner" & provide less turbo protection than M1 0W-40!! The best turbo-protecting synthetic oil you can use all year long in your climate is 15W-50. (As long as it doesn't get below +20°F, you're fine.) Colder than that (regular drops down to 0°F) & 5W-40 would cold-flow better but still offer great turbo protection. Colder still (maybe routine minus-20°F mornings) & 0W-40 would be your first choice. For Saab turbos, you really want to stay with an ACEA A3 rated oil. This is the most durable High Temperature/High Shear (HT/HS) classification, & ensures the oil will survive the harsh environment of your turbo. Operating at well over 400°F & 100k rpm, turbos are the definition of HT/HS! Any of these three Mobil 1 oils (or comparable oils from Amsoil) are your best bets.
Auto-Rx is good & safe to use. I wouldn't recommend any other oil treatments or additives.
posted by 146.82.1...
If you know about Auto-Rx, maybe you already know about Bob...
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