Re: Synthetic Leaks

["Rich Wagner" <drsavage@domain.elided>]

Ron wrote:

>Granted, in a race motor you may see a little more power. In an air coole=
>d
>motor like the Guzzi's (or a VW or Porsche) that can get really hot in th=
>e
>summer, in a car that doesn't get it's oil changed very often, or in a
>"special" car that doesn't get driven very often, you may see a little le=
>ss
>sludge and varnish. In a car that sits outside in sub zero weather you ma=
>y
>get easier starting. For a normal, water cooled, street motor that gets
>regular maintenance, though, I think MOST people using synthetics are
>kidding themselves, but that's just my opinion.

Actually Ron, you will see TONS less sludge and deposits forming.  I have a
car that's been running on Amsoil for 160,000 miles.  (With oil and filter
changes every 12,000.)  It has no sludge in it at all.  None.  Zilch. 
Nada.  Neither on the top end nor bottom end.  (I've recently looked at
both.)  Mineral oils are all formulated from a base.  Most are tar-based. 
"Pennsylvania grade" oils, like Quaker State, Pennzoil, and Wolf's Head are
formulated from a paraffin base.  Going from something like Castrol to
Pennzoil, you will notice a significant difference in the amount and type
of sludging inside an engine.  Going from any mineral oil to a synthetic,
which doesn't have a base, but is synthesized from esters, you will
experience something just short of a miracle.

The other, and more important reason for using a synthetic (the reason
Mobil was contracted to develop the first synthetic by DOD), is that
synthetics can be made to exhibit a specific, <intrinsic>, positive
viscosity gradient.  Most mineral oils have intrinsically <negative>
viscosity gradients.  The hotter they get, the lower their viscosity
becomes.  To make them usable in an engine, a "viscosity improver" (VI), a
long-chain polymer, is added.  The hotter a VI gets, the longer the chains
get, thus increasing the viscosity of the oil.  The problem is, where the
oil does its most important work, in the clearance gap of a bearing, it
experiences a velocity gradient.  At the bearing, the oil is standing
still.  At the shaft, it's moving with the shaft.  This gradient causes a
constant shear stress in the oil film between the two surfaces.  When the
gradient gets high enough, in other words, when the RPM gets high enough,
the shear stress exceeds the ultimate stress of the polymer chains in the
VI.  This breaks the chains, making them shorter, and reducing the
viscosity of that film of oil.  This is the reason that mineral oils come
out of an engine with a lower viscosity than they had when they went in. 
In fact, at high RPM, it's very common to see the oil in the clearance gap
exhibiting a <much> lower viscosity than the oil in the pan.  The faster
and hotter an engine is run, the more important this phenomenon is.  When
you get to jet engine (or Formula 1) speeds, the VI does absolutely
nothing, and you end up with base-weight oil doing all of the lubrication. 
Straight-weight and synthetic oils don't exhibit this behavior.  For the
most part, they maintain the same viscosity throughout their usable
lifespans and, most importantly, in the shear zones.  However, synthetics
also have the added advantage of being multi-viscosity, making them even
better for your engine.


Rich Wagner
Montrose, CO
'82 GTV6 Balocco

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