Why has M1 10w-30 shown to be better then 5w-30?

[buster]

I'm trying to figure out why Mobil 1 10w-30 is better then 5w-30? There practically the same oil but from all the UOA's, it seems the 10w-30 is better. It's not much different. [ July 06, 2003, 01:03 AM: Message edited by: buster ]

 

[J]

quote:

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Originally posted by buster: I'm trying to figure out why Mobil 1 10w-30 is better then 5w-30? There practically the same oil but from all the UOA's, it seems the 10w-30 is better. It's not much different.

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10W-30 has almost no VII to help it cover the 20pt spread. 5W-30 needs a little viscosity index improvement to help it cover 25pt spread. Jae

 

[Al]

But also until the engine gets up to operating temperature the 10W will be slightly thicker. That probably results in less wear.

 

[Whimsey]

Al, Unless you have an engine with "loose" clearances I would think that a thinner oil, ie, 5Wxx vs 10W/15W/20W/xx would cause less engine wear because in a "cold" engine it's circulating faster and easier than a thicker oil. Whimsey

 

[buster]

I agree with Whimsey, I think the thinner 5w/0w-30's from M1 have there place in the newer, tightly built jap engines etc. I do tend to think though, that Mobil's VII's are more on the volative side then other brands. I have no idea how the 0w-40 does so well though.

 

[Al]

But on the other hand-neither the 5W or 10W oil will get to the bearings for a couple dozen rpms. And the 10W oil left behind probably lubricates better than the 5W oil. Just a thought.

 

[Whimsey]

With a cold engine chances are both the 5W and 10w have pretty much drained back to the pan, when using the same brand/quality oil. I still believe the 5W will still get to the parts faster and easier than the 10W upon cold starting. If your engine calls for 10W-30 I'm not saying use 5W-30. But if your engine calls for 5W-30, especially if it's an OHC engine, you're probably best off sticking with the 5W-30. Whimsey