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From: pnovak@ihuxm.UUCP (paul novak)
Newsgroups: net.auto.tech
Subject: Re: What motor oil should I use?
Message-ID: <1337@ihuxm.UUCP>
Date: Mon, 18-Nov-85 15:35:17 EST
Article-I.D.: ihuxm.1337
Posted: Mon Nov 18 15:35:17 1985
Date-Received: Tue, 19-Nov-85 04:27:59 EST
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some recent postings have touched on GM's 5W-30/10W-30 oil recommendation,
and left the impression that GM is doing this because it is better for
your engine.  don't believe it.  what changed over a year ago is the
EPA's regarding manufacturers oil recommendations.  previously, a 
manufacturer could submit a car for EPA mileage testing with any
oil in it and then recommend a different oil in the owner's manual.
this is exactly what GM did: used 5W-30 oil for EPA mileage tests
and recommending 10W-40 in the manual.  Why?  because the lower
viscosity of 30 weight got epsilon more mileage than 40 weight, 
but 40 weight gives better engine protection.  the EPA rule 
change told GM to recommend the oil they submitted for mileage testing 
in the owners manual.  GM could either have submitted cars with
10W-40 or recommended 5W-30.   only after the epa rule change did
GM begin to circulate the cover story that 30 weight oil was better
for your engine than 40 weight.

popular mechanics had an article on the subject in the past year.
their recommendation was to use the manufacturers recommended oil
during the warranty period, and to use 10W-40 after the warranty
period because it provided better protection.

on cold chicago winter days, i'm glad that GM is forcing oil companies to
produce 5W oil: it's becoming much more obtainable.  but i wish they
wouldn't lie about 30 wight oil being better than 40 weight.


paul novak ihuxm!pnovak