Re: [alfa] Mixing Oil Viscosities

["Paul Bayly" <thebaylys@xxxxxxxxxxx>]

----- Original Message -----
From: <JimboMGA@domain.elided>
To: <alfa@domain.elided>
Sent: Saturday, January 17, 2004 9:08 PM
Subject: [alfa] Mixing Oil Viscosities


> Hey Alfa Folks,
> What if a person were to custom mix off the shelf motor oils to get their
oil
> pressure gauge up outta the panic zone?


Jimbo, my view only so take it with a grain of whatever:

I wouldn't attempt to 'cut' your own oil.  If you must play, why not add a
specialised oil stabilizer to your oil.  Me, I'd just change the oil I'm
using.

I doubt your idea would work anyway, though I have no science to say why
except that a 50/50 blend would dilute the rating of the oil accordingly.
So, a straight 10 weight oil mixed with a straight 50 weight oil doesn't
give you a 30.    The 50 oil is still going to act like a 50 oil when the
engine is cold so half your oil is too thick.  The 10 is still 10 when hot
so half your oil is too thin.

 With modern multi viscosity lubricants available today all you need do is
pick one to suit your requirements.  These oils aren't simply a blend of
different weight oils, the entire volume of oil changes viscosity with
temperature.  So a 10W-50 is ALL 10 cold, and ALL 50 hot (near enough
anyway).   I live in a place where we never see temps below 15 deg
centigrade so I can safely use an oil with a cold rating of up to 20W.  As
it gets rather hot most days (and we have no speed limit), I use Penrite
HPR-15 which is a 15W-60.  15 cold and 60 hot.  Covers all bases.

In my experience the oil pressure stays up better with higher viscosity oil
(thicker), opposite to what you experience.  Note that oil pressure itself
is not the be-all of lubrication.  A fully synthetic oil of similar grade to
a mineral oil will likely give lower oil pressure readings, but it will
definitely lubricate better, longer, and probably show more consistent
pressure throughout the temperature range.   Grease has a high viscosity
index and would increase the pressure gauge reading, but it's hardly a
substitute for oil even in a worn engine !

Beatle
Oz
'67 Duetto
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