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with all the weights of oils, I can never remember which designates thicker weight.
Is 30W thicker than 40W?

Also was wondering what the W means. Someone told me once that 10W30 means that the viscosity remains the same in the winter, and that the W stood for Winter.

Was just wondering.
 

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40W is thicker then 30W.

I'm not a chemist, So I wont/can't get into detail on the explanation of the second part.

Besides, I did NOT stay at a Holiday Inn last night..
 

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Check again... 10W is cold flow equivalent viscosity, 30 or 40 is the hot equivalent viscosity of a single grade oil .(hot meaning operating temperature (180 - 200 deg.)

Since a thinner oil flows better when it cold, multi-viscosity oil protect better during a start-up.

Least, thats how I learned it.

..Multigrade oils typically begin as base oils, such as 10W. Then viscosity-index modifiers (polymers) are added in an effort to stabilize the viscosity. This allows a 10W40 oil to flow like a 10W at cold temperatures and a 40W at higher temperatures.

The multigrade oils' viscosity modifiers are long-chain molecules that lessen the change of viscosity with temperature variance. In the past, the polymer additives (used to thicken the oil) were sometimes susceptible to viscosity loss. Permanent viscosity loss occurred when high shear forces (such as the relationship between the main bearings and the crankshaft) actually break the polymer molecules into less-effective smaller pieces. On a similar note, temporary viscosity loss also occurred when the polymer molecules aligned themselves in order to create a path of least resistance.

Fortunately, today's additive packages have improved oil's shear-resistance. However, oils with the same rating from different manufacturers can exhibit different viscosity ratings in an operating engine, depending on the shear stability of their viscosity-modifying additives...
<font size=-1>[ This Message was edited by: Beoweolf on 9/4/06 11:03am ]</font>
 
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