Any truth to this viscosity explanation....?

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Originally Posted By: mechtech2
I knew the density of water changed with temperature, but I had no idea the viscosity ranged so much for plain H2O.


It's not very much of a change. If you torture a VI calculator into giving a VI for water it's about 440. With those low viscosity numbers and fantastic VI, the 0W-20 folk will be wetting their pants with joy.
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Plus, you can make real Kool-Aide with the stuff.

I've designed journal bearing that run on water, but not for engines
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Quote:
"EXAMPLE 10w-30

10=The pumping equivalent of the oil at 32 degrees F. (0c) in comparision to water (water being of "0" Weight)

30=The pumping equivalent of the oil at 212 degrees F. (100c) in comparison to water (water being "0" weight)

Keeping this in mind a "0" weight oil would pump as readily as water, a "30" weight oil would pump as readily as 30 times the "thickness" (or viscosity) of water."



Well, it was a nice story ..and you told it so well - lady at the bus stop sitting next to Forest Gump
 
Originally Posted By: SpitfireS
Originally Posted By: ekpolk
In my opinion, oils should be labeled with hot vis, cold vis, and minimum temp at which the oil may be used.

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What about car manuals?
How would/should they tell you what oil to use?

550W-750W / 9.6-12.5 ?

And why would the not recommend 400W?
The lower the better right?

The oil bottle should have a sort of shear stability or HTHS on it too I suppose or is SM / ACEA A5 enough for that?

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No, you're making to too complex, having presumably allowed SAE ranges to infect your thinking.

The manual should say something like 8-10 cSt hot, and 50-60 cSt cold.

Our present SAE system makes no direct allowance for HTHS vis, so a new simpler system would not, presumably, have to do so either.
 
Ekpolk "The manual should say something like 8-10 cSt hot, and 50-60 cSt cold"


By cold I do you mean 50-60 cSt at 40C? Of course 40C is not cold at all. If you mean 0C then 50-60 cSt is currently a physical impossibility.
The example I gave of PP 0W-20, admittedly one of the lightest SM oils on the market has a kinematic vis at 0C of approximately 300 cSt using the Widman Viscosity Calculator.
 
People just need to understand that it means "thickens less" and "thins less" instead of "It's thinner when cold and thicker when hot". That's the only thing missing in the mind of someone looking at a bottle of room temperature oil.
 
But guys you have to admit the SAE grade numbers mean nothing in and of themselves. If you're going to use numbers, have them mean something.

Secondly, since a bigger number mean a thicker oil, the first number of an SAE grade should be bigger than the second number.
The current system is anti-intuitive.
I know a lot of newbies or lay people who actually think that since the second number is bigger and that it represents a higher temperature, that multigrade oil actually gets thicker at higher temps.

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