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None whatsoever. Detergent oil will turn a dark blue-black after it is heated. Non-detergent oil will turn a reddish-brown. Most diesel engines will turn oil black in the first few minutes of running time. The only accurate way to determine an oil's lubricating value or contamination level is through oil analysis or a portable oil quality analysis. Keeping a good schedule of maintenance goes a long way in keeping your oil uncontaminated.