5W-30 vs 10W-30 start up viscosity

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what's important is the viscosity at 0 degrees c, or 10 degrees c. by 40 degrees, they all extremely watery, and resemble oil. at 10 degrees the 10w30 is like honey.
 

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 Originally Posted By: scoobie
what's important is the viscosity at 0 degrees c, or 10 degrees c. by 40 degrees, they all extremely watery, and resemble oil. at 10 degrees the 10w30 is like honey.
I've got one you'll like At 15C, Castrol GTX 5w30 is thicker than Mobil 1 5w40. At -35C, Castrol GTX 5w30 is almost TWICE as thick as Mobil 1 5w40. So then one must delve into the differences between oils "5w" ratings and the differences in this area between conventional oils and synthetics.
 
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I don't believe there can be any given answer to the comparison. Conventional oil is a natural resource and by rights when something is natural has limits. Being a natural resource will react differently to different conditions, climate, work load, etc. Sythetic oil is engineered from the ground up in laboratories with men in white coats- that formulated synthetic elements to act with oil like properties without the natural molecule breakdown of natural oil due to the extremes.
 
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Umm, ok. How about -30f? I just did some numbers for a post, RTS 5w-40 was 6800cP at -30f while PP 10w-30 was 3990cP. Don't go by the w rating itself until you look at all the actual viscs. It's w-rating plus op visc to get a feel for the oil's visc. This is why AGAIN I say we need some good comparative visc graphs. Some visc curves cross twice!
 
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We can't assume the composition of the oil will result in a straight line graph from 0 C to 100 C. So it should be expected that oils will have variances in between. BTW, I frequently start my car at 40C.
 
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