I've been dumping new oil residue from quarts of QSUD and PP into a jar over the past couple changes. Some 0w20 and 5w20 and 5w30. Mostly QSUD with a little PP. Before the pp it was a homogeneous translucent honey but darkened significantly as well as developed some bubbles and a slight milky tracing after adding PP. Interesting, doubt it has any significance though.
Top jar is new M1 75w90.
Top jar is new M1 75w90.