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From: unpfc1@whuxl.UUCP (CALL)
Newsgroups: net.auto.tech
Subject: Re: Re: What motor oil should I use?
Message-ID: <829@whuxl.UUCP>
Date: Mon, 18-Nov-85 17:30:00 EST
Article-I.D.: whuxl.829
Posted: Mon Nov 18 17:30:00 1985
Date-Received: Tue, 19-Nov-85 03:49:04 EST
References: <561@ihwpt.UUCP> <2435@cal-dbb.fluke.UUCP> <822@whuxl.UUCP> <322@mhuxl.UUCP>
Distribution: na
Organization: AT&T Bell Laboratories, Whippany
Lines: 48

> ****                                                                 ****
> From the keys of Steve Henning, AT&T Bell Labs, Reading, PA mhuxl!smh
> 
> > HISTORY OF MOTOR OIL 
> > Quoted from RIDERANNUAL - 1984
> 
> Thanks for this excellent article on SA-SF and CA-CD etc.  BRAVO...
> 
> Question:
> I have an air-cooled garden tractor engine that turns oil into "tar".
> Previously I used Sears Spectrum 10W-30 and it would turn to a thick tar 
> like substance which took an hour to drain a quart from the crankcase. Now
> I use Quaker State 20W-50 motorcycle oil. The  motorcycle oil is stable.
> Both oils are SD-SF:CC.  Why is the motorcycle oil much more temperature
> stable or is temperature stability something not rated?
*** REPLACE THIS LINE WITH YOUR MESSAGE ***
The reasons motor oil turns to a "thick tar-like substance" is at best
a complicated affair brought on by a combination of conditions which
include: operating the engine at *less than* optimum temperature
and too many operating hours between oil changes. In the first case the 
mixture will be richer and the combustion more incomplete. More by-product
acids, unburned fuel and burned fuel deposits are deposited in the motor-oil.
After a short period of time, the detergents and dispersents present in 
today's oils(they help keep the 
crud in suspension) are used up, and the oil starts to gum things up.
Worn rings have much the same effect on oils.

Also, the molecules in oil wear out, combining with oxygen in a slow
burning process. As the oil molecules attach themselves to more oxygen
molecules, they get thicker -ie. they get larger and larger. 

So, oil that is saturated with deposits and has been largely oxidized
comes out very dark and very thick. Engines that are operated at higher
than normal temperatures (lean gas air-gas mixture) oxidize oils more
quickly despite additives to prevent molecular breakdown.

Motocycle oil is formulated to deal with ranges of temperatures and 
other unique operating parameters(motorcycle
oils are designed to lubricate transmissions *and*
engine parts at the same time) not found in the automotive world
and is therefore superior to automotive oils (and sells for a superior
price). This may be the reason why it doesn't breakdown as quickly 
in your mower. 

But all oil does eventually "die" so change it often.

	Pete Call
	Bell Labs - Morristown