Sludge and lubricants

[Grant Lenahan]

Again, i mostly agree, and strongly agree that what we have all  
ignored is the duty cycle.  Long trips, lean (or correct mixtures) and  
infrequent strats/stops make life easy on oil.  The reverse leads to  
the dilution and contamination you refer to. Totally agree, and  
clearly you have some experience here.

however, you wrote one thing that is not entirely true.  You wrote:

> One thing that many misunderstand is that oil does not wear out...  
> is simply
> becomes contaminated resulting in diminished lubricity...

It does become contaminated, but it also wears out. Or, as i noted in  
a previous post, most oil does. That's because most oils, including  
many synthetics ( think 5w50) require VI improvers to achieve their  
wide viscosity ranges. These VI improvers are long-chain, temperature- 
dependent molecules that unfold at higher temperatures to raise the  
viscosity or an otherwise thin base. They most certainly do wear out,  
shearing (so the higher number is no longer met) and also congealing  
in heat after shearing (one of the causes of sludge). I have the  
luxury of socially chatting with major oil formulation engineers, and  
they cringe at the marketing claims for their own products in many  
cases.

Overall, though, your points are spot on.  Service interval = f(duty  
cycle).  And a good narrow-range synthetic will perform for very long  
periods indeed.  e.g.: 10w30 >> 5w40. Alas, that wider range is highly  
beneficial in many instances.  Normally driven, naturally aspirated  
motors, though, are not among them.

As an aside, synthetic fuels were also pioneered by wartime germany  
for the same reason - they were being cut off from the supplies of oil  
that ran their war machine.  Hence the importance of Rommel's mission!

I think we have just passed from useful info into "glazed eyes" however.

Grant