[T3] ZDDP...again

[Jim Adney]

On 17 May 2011 at 20:24, Keith Park wrote:

> All the multi vis oils have viscosity enhancers, its what makes them
> multi-vis.  Basically, the  rule of thumb is to use the oil viscosity that
> gives you 10PSI for every 1000RPM of engine speed, and not worry too much
> about idle.

Viscosity enhancers just level the viscosity vs. temp curve, making 
one oil work well over a larger temp range. If you don't have the 
wide range of temps, then there's no advantage to the capability. In 
fact, the enhancers break down in use, leaving you with a lighter oil 
than you thought you had. So 10W-40, when it breaks down, leaves you 
with something like SAE 10W, which is not what you'd like to be 
driving in the summer months.

OTOH, SAE 30 is always SAE 30, never breaks down (although the 
additive package wears out, just like any other oil) and is not 
dependent on an additive to maintain its viscosity.  

-- 
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Jim Adney, jadney at vwtype3.org
Madison, Wisconsin, USA
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