<VV> Awl - OY!

[Padgett]

At 10:26 PM 7/3/2005, you wrote:
>Oil will decrease in viscosity when heated. Multigrade oils have an additive
>package that includes a viscosity stabilizer that reduces the amount of
>viscosity decrease as the oil gets hotter. This is measured by the 
>viscosity index
>(VI).

Correct

>However, over hours of use, the oil tends to thin less and less as this
>package is used up. That's another way of saying that the hot oil gets 
>thicker
>after considerable use.

That's an over generalization. As the long chain polymers in the additive 
package break down over time, a multigrade will approach the viscosity of 
the base stock. This means it will be *thinner* hot than when fresh. (logic 
says it will also be thicker cold than original also but I never checked that).

For many years I knew when it was time to change the oil when the hot 
cruise pressure dropped by 2-4 psi. After changing the oil and filter it 
always came back up. Suppose I might have been seeing buildup in the oil 
filter which I always change with the oil, but have never seen anything 
concerning that.

Padgett