When you initially change after a long time with one type of oil, it's not uncommon for some consumption to occur even on a good engine that isn't normally leaking or burning oil. I've never seen a good explanation for why it happens, but a lot of people have commented on it over the years.
When this happens, some people immediately switch back to their old oil, and some don't. The people who switch back see the consumption stop, and then start talking about how their car doesn't like the other oil. Those who stick with the new oil see the consumption continue to decrease until the car is back to normal, and continue to use the new oil.
Like I said, i've never seen any explanation for why it occurs, but the consumption goes away after an OCI or two.
Now I vaguely remember someone posting on here in the last 6 months about how they did some tests on the fleet of vehicles at work, and did UOAs with them. They had some cars that had convention, some had synthetic, some did shorter OCIs, some did longer, some changed brands, some stayed the same, etc. If I recall they were pretty consistent with what they did with each vehicle and did UOAs with them. The surprising thing was, the lower wear numbers wasn't with the vehicles that you expected, their results were that the biggest impact was if you changed oil brands or not. By sticking with a quality oil, their (non-scientific, but still very interesting) experiment showed that sticking to one brand of oil had the biggest impact of keeping wear numbers low.
Now like I said, I vaguely remember the thread so I can very well be butchering what was said in it. I'll see if I can find it when I have some more time.
