[Vwdiesel] Candles? Was: Topic limited, or people enabled? And Wheel Bearings.

[Gavrik Peterson]

>I've never really understood the multi-viscosity -vs- 
>straight weight issues...my education is somewhat lacking.

This topic is something I read about years ago in SAE 
papers and in a book on diesel engine lubrication. Some of 
the SAE papers were as early as 1970 and the book was 
published in the 1950s, so I wonder how much things have 
changed.

The main point that I got, was that lube oil is 
non-Newtonian and therefor it's viscosity changes with the 
amount of shear it is experiencing. The viscosity of some 
lube oils can increase by as much as 100,000:1 under high 
shear. This makes lube oil useful because its viscosity is 
low when you need it to flow but gets high when you need 
it to stick around.

The diesel lubrication book showed that the degree to 
which an oil has this valuable property depends on its 
base stock. The SAE papers showed that multi-viscosity 
oils with viscosity improver additives have much less of 
this property. One SAE paper (early 1970s) said that with 
current viscosity improvers a 5w70 oil could be 
constructed. However, the author remarked that an engine 
lubricated with this oil would most likely seize after a 
few minutes of operation.

That's about all I know about this subject. Does anyone 
have more details or know how things stand with the 
current oils?

   --  Gavrik