The weather was bad in the midwest and my daughter needed an oil change this week in her Honda CR-V, 2.4L.. She normally does it herself with M1 and a Fram Filter. Below are pictures of the oil before and after the oil change (spill and fill). Yes, the oil and filter was changed. This is not a dig towards Walmart or any other oil change service. Similar results occur even with DIY service. 1. New Oil in a vile. 2. New oil sampled from sump after 15 miles. 3. Blot test of the new oil after 15 miles and a standard oil change. 4. Blot test of new oil from the sump, after a 99% flush after 20 miles in my car. Blackstone Labs confirmed that in modern engines, up to 20% of oil may remain in an engine. How much of the serviceability of the oil is reduced by mixing with the old oil? What impact to the the longer term engine life due to the remaining old oil? Can that remaining oil last another full OCI? If not, I assume the oil will oxidize and causing sludge, varnish, and carbon build-up in the engine.