100dC cST viscosity--is it directly proportional?

[Jeffrey Behr]

Are the numbers truly indicative of thickness? For instance, an SAE-10W oil may have a viscosity of 5 while an SAE-40 oil could have a vis of 15 (from BITOG's viscosity chart at http://www.bobistheoilguy.com/visc.html ). Does that mean that X units of this SAE 40 oil will take 3 times as long to drip thru an orifice compared with that SAE-10W oil?

 

[jorton]

This is my interpretation for actual viscosity at 100cst. It may be inaccurate but I see no one else has answered yet.

No, not at 100c.

10w is not the viscosity at 100cst. It is the "winter rating" for multi-grade oils at very low ambient temps. SAE 40 flows much slower at very low ambient temps. At 100c which is almost max normal operating temp, sae 40 and 10w-40 flow about the same.

 

[bruce381]

Quote:

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Are the numbers truly indicative of thickness? For instance, an SAE-10W oil may have a viscosity of 5 while an SAE-40 oil could have a vis of 15 (from BITOG's viscosity chart at http://www.bobistheoilguy.com/visc.html ). Does that mean that X units of this SAE 40 oil will take 3 times as long to drip thru an orifice compared with that SAE-10W oil?

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I using SUS or saybolt universal seconds test which the time for the oil to drip/run throught an orifice at a set temp then yes.
bruce

 

[mechtech2]

The simple answer is yes, the numbers relate to thickness.
Like mentioned, the first number in a multiweight oil refers to cold and the second to hot characteristics. [0F and 200F] A 30 or 40 weight is not an exact thickness, but a range.

 

[XS650]

Quote:

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The simple answer is yes, the numbers relate to thickness.
Like mentioned, the first number in a multiweight oil refers to cold and the second to hot characteristics. [0F and 200F] A 30 or 40 weight is not an exact thickness, but a range.

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The xW tests hasn't been done at 0F for something like 40 years. They are now 2 different tests done at different temperatures for each viscosity. The high temp test is done at 100C = 212F, but you were close on that one. :cheers"

 

[Jeffrey Behr]

ahem...as indicated in the title, I'm asking about the 100dC cST numbers, boys.

 

[jorton]

Quote:

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This is my interpretation for actual viscosity at 100cst. It may be inaccurate but I see no one else has answered yet.

No, not at 100c.

10w is not the viscosity at 100cst. It is the "winter rating" for multi-grade oils at very low ambient temps. SAE 40 flows much slower at very low ambient temps. At 100c which is almost max normal operating temp, sae 40 and 10w-40 flow about the same.

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Today I was looking at a product data pdf so I now know what sae 10w is. Sorry about my "winter rating" answer, above.