My dad and I bought this car for my mom last year. It had an oil change receipt shortly before the dealer got it with bulk conventional 10w-30. Oil was clean golden and at proper level when we got it, but there was some sludge visible at the top end, and by the end of summer the oil had turned almost black like diesel oil. I drained it out and also found the filter had a pleat blown wide open too, so that couldn't have helped. Put in the M1 10w-30, basic filter, and decided to run it. But now the oil is dark again, much darker than my car at 4k and my dad's car at 5k. I know oil color may not mean much, so I pulled a sample to get it checked out before I threw away good oil. Where the heck is all that iron coming from? Everything else seems fine except for the insolubles starting to get high with a relatively short interval. This car does see some short trips, but is not getting thrashed on. It used zero oil in those 3k miles. Only thing I could think of for iron source is possible debris getting in the cylinders when I replaced spark plugs. I cleaned the wells before removing plugs, but I could see a bunch of crud inside when I used my inspection camera to check the piston crowns. I vacuumed the cylinders out until I couldn't see the crud in the camera anymore before replacing the plugs. It idled better than ever with fresh plugs and drove fine since. Will change this oil and filter soon then sample again in 3k or so. What are your thoughts?