0-30 is thick?

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Jun 3, 2004
I have heard this a few times....that GC is thick oil compared to others of the same weight. So, is the "O" accurate?...meaning, does it start out nice and thin as an "O" would indicate? At the thicker end (30), is it actually more comparable to the 40 end of things? If so, why do they call it 30? Kelton
The easiest way to think of this is to think of there being 10 different oils between Xw-30 & Xw-40. All of these oils fall into the Xw-30 class. They are Xw-30, 31, 32, 33,...., 38, & 39. GC probably falls somewhere in the Xw-38 range. Therefore, it is still a 30 weight, but thinker than all of the other Xw-30 oils that fall into the 31, 32, 33, etc... range. As far as the cold pumpability of the oil, yes it does fall into the 0w class of oils.
As you can see from the link VaderSS posted xW-30 oils fall into the viscosity range of 9.3 < 12.5 GC has viscosity of 12.2 cSt at 100C, so if it were just a bit thicker it would be classed as a xW-40 oil, hence why people refer to it as being a thick 30 weight.
Originally posted by Audi Junkie: It's also a "thick" 30 because it does not shear.
So, given that shear resistance, it makes a good summer oil, even though the 0w- means it has to use alot of VI improvers? I have it in my car right now, and it's getting HOT down here in Tx. I've heard that oils with high VII tend to shear moreso than oils with less...so is GC the exception to that rule? [I dont know]
bighead, GC is the exception to the rule, because of the trick mixture of exotic base oils, it needs no viscosity index improvers! This is why it's so shear stable.
Let's be careful here, GC is a thick oil at "normal" cold temps, it is materially thicker than M1 5w30 at maybe 10F. At -35F GC may be thinner than M1 5w30. At operating temps GC is almost a 40w oil whereas M1 5w30 is in the mid to lower part of the 30w range. I tested GC against Citgo dino 5w30 at 10F, Citgo dino was much thinner at 10F than GC. Let me be clear, GC was not so thick to be usable, it was just materially thicker than the Citgo dino 5w30.
I think the point is, you can't look at two numbers and expect all oils with those same two numbers to be anything near the same, except at the temperatures those two numbers are derived at. Even then, it's just a "ballpark" and a rather large one at that...
Originally posted by kevm14: Yeah, thicker at 10°F. Try them at 30 below.
Does it get -30F in RI? [I dont know]
Not where I am, but I was just pointing out why one has a 5 rating and the other is 0. Sometimes it has no bearing on the conditions the car sees.
Originally posted by kevm14: Sometimes it has no bearing on the conditions the car sees.
but it could have a bearing on the bearings...yup [Big Grin]
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