<VV> Re: viscosity vs temp

[BobHelt at aol.com]

In a message dated 7/3/05 4:33:45 PM US Mountain Standard Time, jld at wk.net 
writes:

> I reiterate current synthetic motor oil of the SL and SM variety get 
> thicker with heat cycles. 

It would appear that the two different opinions on this subject are not 
talking about the same thing. Sort of comparing apples and oranges. Here is what 
happens:

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).

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. Again, that's why the API has a max vis increase spec.

Regards,
Bob Helt