Date: Thu, 14 Sep 2006 14:06:23 -0400
From: "gw" <>
Subject: Re: oil sludge?

"darthpup" <> wrote in message > And your point is what Fred? > I believe his point was that you're incorrect. Multi viscosity oils do not "thicken" under high temperature. The added polymers decrease the base oil's tendency to thin out at high temperature, thus maintaining the lubricating properties of a thicker oil. The problem occurs when an oil with a large viscosity spread - such as 10W50 is used. There is so much polymer in this mixture that it is subject to excessive thermal breakdown, thinning back to it's 10 weight base when hot. Your case points to cheap oil or excessive oil change intervals. 5w30: Has a 5 weight oil base, but will not thin more than a 30 weight oil would at 100C. That does not mean that it will thicken to the viscosity of 30 weight oil, just that it will not be any thinner than 30 weight oil would be at the same temperature. A straight weight 30 oil will be thick at low temperatures, when the engine needs a thin oil to flow quickly, and it will thin out considerably at high temperatures, when bearings need the thicker oil film. The polymers added to multi-viscosity oils help prevent that huge viscosity swing - exactly the opposite of what you said.

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