Relay-Version: version B 2.10 5/3/83; site utzoo.UUCP
Posting-Version: version B 2.10 5/26/83; site ihuxn.UUCP
Path: utzoo!linus!decvax!harpo!eagle!mhuxt!mhuxi!mhuxa!houxm!ihnp4!ihuxn!res
From: res@ihuxn.UUCP
Newsgroups: net.auto
Subject: Re: Magic Oil Numbers
Message-ID: <317@ihuxn.UUCP>
Date: Tue, 16-Aug-83 23:42:55 EDT
Article-I.D.: ihuxn.317
Posted: Tue Aug 16 23:42:55 1983
Date-Received: Wed, 17-Aug-83 07:28:04 EDT
References: <2598@rochester.UUCP>
Organization: BTL Naperville, Il.
Lines: 33

With reference to the difference between, say, 20 and 20W oil:

There are two temperatures at which the viscosity of motor oil is
measured.  If memory serves me right (flames to /dev/null if not!)
these temperatures are 0 degrees F and 100 degrees F (the latter
temperature I am unsure of ... read these two temperatures as "cold"
and "hot").  Hence, 20W oil has 20-weight viscosity at the lower
temperature, while 20 (no W) oil has 20-weight viscosity at the higher
temperature.  Further, 10W40 oil has 10-weight viscosity at the lower
temperature, and 40-weight viscosity at the higher temperature.

As to the significance of 10W30 vs. 10W40 vs. 20W50 etc.  The higher 
the number value (the weight) of the oil the thicker it is.  Hence, 
20W50 is thicker at all temperatures than 10W40.  For operation of
today's high-engine-temperature cars it would appear that 20W50, then
10W40, then 10W30 would be the order of preference ... however, for a
fairly new car (still pretty tight clearances) it will be easier on the
starter in the winter if a lighter grade (10Wxx or 5Wxx) oil is used in
the northern part of the country.

As a side comment ... I once had a friend who had a very old (beater,
not antique) car that burned more oil than gas ( :-) for those of you
who cannot recognize an innocent exaggeration and would flame me
otherwise!).  One day he announced that he had solved the problem -- he
had switched to something like 90-weight oil.  It worked great ... oil
consumption went down to zip.  Then the year worked its way around to
winter and the temperature (in normally tropical Detroit, MI) fell out
of the bottom of the thermometer.  Have you ever tried to start a car
when the oil has the viscosity of rock candy?  He took the bus until
the middle of March that semester!

					Rich Strebendt
					...!ihnp4!ihuxn!res