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From: paulhus@euclid.DEC (Chris Paulhus 223-6871 MLO8-3/T13)
Newsgroups: net.auto
Subject: Transmission Lubricants
Message-ID: <222@decwrl.UUCP>
Date: Wed, 12-Dec-84 12:17:41 EST
Article-I.D.: decwrl.222
Posted: Wed Dec 12 12:17:41 1984
Date-Received: Fri, 14-Dec-84 04:36:07 EST
Sender: daemon@decwrl.UUCP
Organization: DEC Engineering Network
Lines: 45


	A few comments on transmission lubricants:

	Originally (say 1950's and 1960's) manual transmissions used an
	EP rated oil, the EP standing for resistance to extreme pressure
	which occurs at the gear tooth contact point. In the late '70's,
	GM decided that	stocking two fluids, an automatic transmission fluid 
	(ATF) and an EP fluid was too much trouble for their dealers and 
	redesigned their manual transmissions to allow ATF to function as a 
	lube. ATF also has viscosity improvers that allow it to function 
	better at low temperatures, similar to multi-grade motor oils.  
	
	The EP rated oil was given a viscosity range rating higher than
	motor oils (despite having the same real viscosity range : a 90 EP
	oil has about the same viscosity as a 40 weight single grade motor
	oil!) so the two products wouldn't be confused  (like us acoustics
	types are using decibels for sound pressure and Bels for sound power).

	So, a 10W-40 motor oil is similar to the 90 weight EP transmission
	lube of old, less the extreme pressure additives (but the new SE and
	SF motor oils do pretty good on this score), but with superior low
	temperature performance.  

	Viscosity improvers (VIs) are long chained polymeric (sp?) molecules 
	that coil up when cold and add nothing to the base stock's viscosity. 
	As they warm up, they uncoil into thread-like strands. This effectively
	increases the viscosity of the mixture (base stock plus viscosity
	improvers).  In highly stressed engines (high contact pressures, lots
	of shear stress at the lubricated surfaces -  typical of higher rpm,
	smaller engines) there was a tendency for the long thread-like 
	VIs to be sheared or cut, decreasing their effectiveness.
	After 20,000 miles your 10W-40 ended up with a bunch of chopped up
	VIs in a base stock of 10W oil, which didn't provide adequate
	protection at 180 deg. F (or more in VWs and such!).  (Remember, the
	40 weight is just the effect of the VIs on the base 10W stock.)
	This situation is better now than it was 20 years ago, but users
	of multi-grade motor oils - especially high rpm users - should be
	cautioned to obey the frequent drain intervals recommended.  (The
	other reason for frequent drain is the breakdown of the other neat
	additives in the oil - anti-rust, anti-foam, anti-acid, etc.  This
	is particularly important if the oil doesn't get up to temperature
	and volatize off the acids and other bad stuff.)

	Another 2 cents worth from: N. Chris Paulhus DEC-Maynard
				    decwrl!euclid!paulhus (617) 493-6871