Should we be using lighter weight oil?

George Harris harchris at
Tue Dec 31 10:38:40 EST 2002

I believe that the viscosity rating on the can is at a specific
temperature. In Greg's example he compared the oils at 5 deg. F. We know
from the synthetic oil hoopla that the viscosity is more stable in
synthetics so perhaps it doesn't thicken up as much as regular oil.

Although one comment I have is to the fellow who mixes regular and
synthetic; When I was considering changing my motorcycle to synthetic a
knowledgeable fellow enthusiast told me to flush the engine with
kerosene to get all the old oil out. He said that mixing the two would
cause clotting. I witnessed this in another engine that wasn't cleaned
out ... an oil passageway clogged with a thick gel of oil. Not pretty.
Ever since I have been paranoid about mixing the two types.


"Dave K." wrote:
> What I can't understand is why a synthetic oil of the same viscosity flows
> more easily than a dino oil of the same viscosity at any given temperature.
> Viscosity IS flow, so what gives?
> Dave K.
> '90 CQ
> ----- Original Message -----
> From: "George Harris" <harchris at>
> To: <Greg.Roa at Cinergy.COM>; <quattro at>
> Sent: Monday, December 30, 2002 7:43 PM
> Subject: RE: Should we be using lighter weight oil?
> > > That says it all for me.  I like numbers as much as the next engineer,
> but
> > > a 5w rating doesn't mean much to me if my engine can't pump it in the
> morning.
> >
> > Aren't you comparing Apples (regular oil) and Oranges (synthetic)? Now
> > try comparing the flow of 0W40 and 15W50 at the same temperature. In my
> > experience any oil, including the 10W50 synthetic that I use, is pretty
> > thin at operating temperatures. I think you want that flowability when
> > you first start the car at 5 deg F.
> >
> > Cheers
> > George

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