Originally Posted By: milwaukee
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You guys are dealing in subjective feelings not facts. The difference is so small between 5-20 and 5-30 that any difference you can hear between those weights in the same brand is non existant.
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I'm sorry, but it is you who is being un-factual. First, you overlook that 5w-20 and 5w-30 are not set points, but instead, represent broad ranges of viscosities. If you have a 20 wt that's very thick for the grade, and a 30 that's very thin, well, maybe on viscosity alone, you're right. Two oils, one testing at 9.2 cSt, and the next testing at 9.5 cSt would be a 20 and a 30 respectively, and on that basis, would be virtually indistinguishable (though they might be very different when considering the base oils used and add pack). By contrast, another two oils might test at 5.6 cSt and 12.5 cSt respectively, and guess what -- they'd also be a 20 and a 30 respectively.
OK, you can't hear a difference in your Yaris -- that's fine. But don't generalize your experience to everyone else. Believe it or not, you're not the center of the universe. The most dramatic difference I've seen was in my 2003.5 Camry V-6. In 04, I switched that car from M1 5w-30 (then being made at around 9.5 cSt) and GC (then, as now, a 12.1 cSt oil). That car had a metallic, "thrashy" sound on the M1 that immediately and totally went away with the heavier GC. No ding at all on M1 (I got great UOA results with the M1), but as far as engine sound was concerned, the GC was in a different league.