Oil Level and Fuel Economy

[Yaris Hilton]

I used lots of Arco Graphite in the '70s and early '80s. Thought it was good stuff.

[yaris-me]

I talked to someone at the can recycling center and he was trying to convince me that changing the filter every 2,000 miles and changing the oil when it gets black was the way to go. I can't buy it for the simple reason that blow-by will break down the oil and also create sludge.

[Yaris Hilton]

Whether oil's black or not doesn't correlate very well with how contaminated it is with acids, fuel and junk or how the additives may have broken down. Black oil can be good oil that's got combustion soot in suspension. If you want to be precise about changing oil by its condition you should subscribe to an oil analysis service. Not wanting to spend the money and energy on that, I'll just change at the factory recommended intervals.

[sbergman27]

Originally Posted by Yaris Hilton

Black oil can be good oil that's got combustion soot in suspension.

The significance of oil color is often misunderstood. Before detergent oils, the soot just settled out wherever it could rest inside the engine. The whole purpose of detergent oils is to keep the combustion byproducts that do make it into the engine safely dissolved in the oil. Sometimes I hear people say that Brand X oil is good because it still looks clean after x number of miles whereas Brand Y looks black. Now... since the quantity of combustion products getting into the engine is likely the same in both cases... where in the engine *is* all that gunk it's not dissolved in the Brand X oil? Answer: In the pan, in various crevices, under the rings, etc.

Of course... all respectable oils today are detergent oils. So the "difference" between brand X and Brand Y colors is likely either imagination or a difference in the driving and conditions between the two samples.

Note that I'm only addressing the color of the oil and not things like varnish, which are an entirely different situation which can very well be quite different between oils.

-Steve

[R2D2]

Originally Posted by Yaris Hilton

Whether oil's black or not doesn't correlate very well with how contaminated it is with acids, fuel and junk or how the additives may have broken down. Black oil can be good oil that's got combustion soot in suspension. If you want to be precise about changing oil by its condition you should subscribe to an oil analysis service. Not wanting to spend the money and energy on that, I'll just change at the factory recommended intervals.

Excellent point, Yaris. Sometimes people forget these points. Oil color is NOT a reliable indicator of the condition of an oil or its suitability for continued service.