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From: cjohnson@zehntel.UUCP (Chris Johnson)
Newsgroups: net.auto
Subject: Re: Multi-Viscosity Oils
Message-ID: <1609@zehntel.UUCP>
Date: Thu, 27-Sep-84 12:48:18 EDT
Article-I.D.: zehntel.1609
Posted: Thu Sep 27 12:48:18 1984
Date-Received: Sat, 29-Sep-84 08:35:42 EDT
References: <131@umcp-cs.UUCP>
Organization: Zehntel Inc., Walnut Creek, CA
Lines: 35

The standard *high* temp is 220 deg. f.   This is important because one of
the major problems with Multi-Vis oils is that as the tempurature varies
*outside* of their intended range they tend to break down faster than 
the corresponding single viscocity oil (ie. 10w30 is worse at 230 degrees
than straight 30 weight.)  In a water cooled engine this isn't that important
because the engine basically won't heat up over 220 degrees, but in an air
cooled engine temps can reach up to 250 degrees in worst cases.  This is 
especially important because as the oils viscosity drops the oil pump 
doesn't work as well.  I owned a VW bug with a *very* tweeked engine and
found that 30 wt oil heated to a point that the engine would regularly
vapor lock due the temp in the engine compartment (it is especially
strange to have dual carbs with one vapor locked).  I switched to 
50 wt racing oil (Valvoline) and the problem disapeared.

Analysis:

     If you own a water colled engine use a multi viscosity oil if your
climate is severe enough to require it.  (30 wt oil is *very* thick at
0 degrees)  If your climate is constantly 40+ degrees use what you want.
Don't use single viscosity 10wt or 20wt oil unless you live in -20 degree
weather AND your car never heats up to operating temp.(ie. you use it 
for short drives only.)

     If you own a air colled engine use the highest viscosity oil you
can *for your climate*.  Change your oil's weight if the weather cools during 
winter.  

      DON'T mix oils of different weights.  The thicker oil will sink to
the bottom of the oil pan and just sit there, inhibiting cooling by
providing an insulating layer (esp air cooled).

     DON'T mix synthetic oils and standard oils for similar reasons.

                             Slipperily yours,
                                   Chris Johnson