Quote:
Originally Posted by Wayne's World
Then what does it correlate to? I always thought any deviation in color from the original was largely due to blowby/carbon/dust suspension in the oil and thermal breakdown. 
You're probably regarded as the subject matter expert on this board so I welcome some ejumacation.  |
You can get colouration from partices that don't contaminate the oil (what I meant by cleanliness was lack of contamination). You can also get contamination from particles that don't change the colour of the oil. Thermal breakdown isn't part of the equation.
Yes, soot colours the oil. If the oil is black, though, then the soot is in suspension, as it is supposed to be. It isn't harming your engine. If you want to keep your oil golden coloured longer, use a non-detergent oil. That won't be as good for your engine as an oil that has detergents, though.
Here is one article (I really don't like Amsoil, primarily due to their business model, but they are right in this paper): Color of Engine Oil
I let my SAE membership lapse, so don't have any access there, but this one came up on a search:
Motor Oils and Engine Lubrication Book: Motor Oil Engineers
The extract from that article makes a good point that some value can be taken from the colour of oil, notably if it has water in it and is therefore a malted-milk colour. I certainly agree with that.
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