Here are the samples of the same oil (Toyota 5w30) from different OCIs and different duty cycles in the same engine.
-Sample on the very left is a brand new oil.
-Next one to the right has 10k kilometers (6200 miles) and 294 hours of mixed driving.
-Third sample has 16k kilometers (10k miles) and 307 hours of highway cruising.
-The darkest sample on the right has ONLY 8.5K kilometers (5.3K miles) and 354 hours of city traffic with idling and stop&go.
Of course a UOA would show a bigger picture, but oil color does give a good idea of how used up the oil is. Free visual oil analysis, so to say.
-Sample on the very left is a brand new oil.
-Next one to the right has 10k kilometers (6200 miles) and 294 hours of mixed driving.
-Third sample has 16k kilometers (10k miles) and 307 hours of highway cruising.
-The darkest sample on the right has ONLY 8.5K kilometers (5.3K miles) and 354 hours of city traffic with idling and stop&go.
Of course a UOA would show a bigger picture, but oil color does give a good idea of how used up the oil is. Free visual oil analysis, so to say.