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wjdunn3 wjdunn3 is offline
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Join Date: Nov 1998
Location: Flowery Branch, GA USA
Posts: 51
The grades are indications of Viscosity. From the Tech Article on this site:
"Another way of looking at multi-vis oils is to think of a 20W-50 as a 20 weight oil that will not thin more than a 50 weight would when hot."
"Viscosity is a measure of the "flowability" of an oil. More specifically, it is the property of an oil to develop and maintain a certain amount of shearing stress dependent on flow, and then to offer continued resistance to flow. Thicker oils generally have a higher viscosity, and thinner oils a lower viscosity."

It is natural for oil to darken with usage. The question is, at 3000 miles of service, is your oil still transparent or has it gotten so dark that it is opaque? At 5000+ miles, mine is somewhat darker than new oil but very much still transparent.
If your oil is getting opaque, then it is sheering and burning (in the tech article this is where the "ash" comes in). This would indicate that the oil is too thin for your application / heat range.
0w-30 is a thinner oil than a 10w-30, not thicker.
As for change interval:
"Synthetics can be run two to three times the mileage of petroleum oils with no problems. They do not react to combustion and combustion by-products to the extent that the dead dinosaur juice does. "
Old 10-19-1999, 06:48 AM
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