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Old 03-19-2021, 02:19 PM   #211
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I certainly agree that if there were an empirical reason to believe that a 0w-40 Dexos 2 oil is somehow worse for our cars than something not specified by GM, then it would make sense to consider using it. For example, that foaming Harley oil you mention sounds like junk! But I am not aware of any evidence to that effect regarding any Dexos 2 oil. The Dexos 2 spec has the most stringent anti-wear criterion in history, so it's not just about protecting your emissions equipment (although that's an important goal, too!). I'm also sure it has some spec for minimal foaming, flash point, and other important properties. If someone has legit info that this spec and viscosity is worse than something else, then we should have that discussion.

Keep in mind that there is at least one other Dexos 2 0w-40 out there, Castrol Edge. Whether it is better than Mobil 1 ESP, I don't know. I have my suspicions that M1 is better, but that's based on old info about how the Castrol synthetics used to be made, and that may be outdated now. So I'm not saying you have to run Mobil 1 - I'm just saying you should run a Dexos 2 0w-40.

One more thought. I think part of the problem comes from people not understanding what the nominal multiweight ratings really mean. People tend to think the nominal viscosity index (e.g. "40w") refer to an actual viscosity measurement, but it's not that simple. That leads to the belief that a 0w-40, for example, gets thicker as it heats up. But that's not true at all. Those numbers aren't absolute viscosity measurements. Just look at the kinematic viscosity ratings I quoted above. Those numbers I referenced are measurements of how resistant to flow (viscous) the oil is. What the nominal viscosity index means is that a 0W-40 behaves like a 0w oil at a low temperature and it behaves like a 40w at 100C. But it is still much thicker at 40C than it is at 100C. It still gets a lot thinner as it heats up, but the spread between its low-temp and high-temp viscosities is just a little smaller than it would be for a 5w-40 or 10w-40. If they could make oil thinner than 0w at cold startup and keep it working well at high temps and high shear forces, you can bet they would, because even a 0w oil is too thick to flow quickly at startup.
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Old 03-19-2021, 05:08 PM   #212
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And I was thinking this morning... I watched my wife get in and start it. And Ive told her she needed to warm this car up a bit more than the lease cars shes been driving... But she barely warmed it up for 30 seconds. And shes really good but if shes late for work shes going.
Ill have her running out of the development in second gear at slightly higher rpm and let everything warm up before hitting the bigger roads... But still its not going to be warmed up until shes half way to work.
So That makes a case for the 0w too.
I also used to run straight 60 Valvoline racing oil in the old Harley for a few years. It constantly ate starter bendixes to the point I was kick starting it all the time. Until I switched to 20w 50.
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Old 03-19-2021, 06:22 PM   #213
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Originally Posted by MR's 2SS View Post
And I was thinking this morning... I watched my wife get in and start it. And Ive told her she needed to warm this car up a bit more than the lease cars shes been driving... But she barely warmed it up for 30 seconds. And shes really good but if shes late for work shes going.
Ill have her running out of the development in second gear at slightly higher rpm and let everything warm up before hitting the bigger roads... But still its not going to be warmed up until shes half way to work.
So That makes a case for the 0w too.
It definitely does. This is more and more of a thing as more cars have the auto-stop feature, too, and with more hybrids running at least a few miles on just battery and then starting the engine sometime mid-trip. That and tighter clearances are a couple reasons why the 0w oils have been developed.
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Old 04-16-2021, 05:24 AM   #214
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FWIW, the Mobil1 0w40 has higher viscosity than 5w30 when cold (and warm).
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Old 04-16-2021, 07:27 AM   #215
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FWIW, the Mobil1 0w40 has higher viscosity than 5w30 when cold (and warm).
Not sure what you mean on that statement, but 0-40 flows like 0 weight oil when cold and has the protection of 40w oil when hot. O weight oil flows better when cold than 5w oil and I would think 40w oil has more viscosity or thicker than 30w oil when hot
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Old 04-16-2021, 12:42 PM   #216
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FWIW, the Mobil1 0w40 has higher viscosity than 5w30 when cold (and warm).
Wrong. The kinematic viscosity of 5w-30 ESP at 40C is 72.8 mm2/s, whereas for the ow-40 it is 69. At 100C the 0w-40's viscosity is higher (12.9 vs 12.1), which is exactly what we'd expect and want.
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