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From: joe@dual.UUCP (Joe Weinstein)
Newsgroups: net.auto.tech
Subject: Re: Mixing oil weights and 10w40
Message-ID: <1184@dual.UUCP>
Date: Tue, 7-Jan-86 13:28:13 EST
Article-I.D.: dual.1184
Posted: Tue Jan  7 13:28:13 1986
Date-Received: Thu, 9-Jan-86 06:21:40 EST
References: <2457@amdahl.UUCP>
Distribution: net
Organization: Dual Systems Corp. Berkeley, Ca.
Lines: 34
Summary: Oil Viscosity Facts...

Hi.	Some facts about oil viscosity and mixing.

	1 - The effect of one viscosity oil on another is
	not linear! A lower viscosity oil will bring down
	the viscosity of the mix even in small percentages.
	Contrastingly, You have to add so much thick oil to
	thicken a mixture that you would need bathtubs and
	bathtubs full of 40 wt. to bring a quart of 30 wt.
	up to near 40 wt. You can test this with a cup of
	30 wt. and some 3-in-1.
	This means that topping up with a heavier oil is OK.
	As soon as they mix the viscosity will be what you had
	before.

	2 - The listed viscosities on cans are in fact ranges
	which can OVERLAP! One dealer's 30 wt. might be sold
	as 40 wt. by another!

	3 - Oil breaks down with ( time X high temperature ).
	A major factor in the temperature of an oil in an
	engine is the viscosity. A thicker oil gets hotter
	owing to shear forces than a thinner one. All oils
	break down at the same temperature. Therefore you should
	use the lightest oil recommended by the engine manufacturer.
	Especially after break-in where surfaces are smooth.

	The additives are more important than the viscosity.
	Use only the best grade ( SF ). Also, molybdenum add ins
	work to coat surfaces and protect them during start-up 
	before the circulation system gets oil there. Start-ups
	account for a lot of the wear of a broken-in engine so
	moly is a good bet.

	Joe Weinstein