In the 1990s I worked in an engine test facility that evaluated lube oils , additives and fuels. A very interesting place.... my boss once said ' it's like putting dracula in charge of a blood bank, having you in there' .
We did some testing of bike 2 stroke oils but nothing else.
But the late 80s and early 90s had big issues with what was called the black death in car engines.....It was thick black stuff with a consistency of hellmans mayonnaise. It was then that oil detergents began to improve. So most oils today have some form of cleaning agent.
But we never tested pre drain cleaners. But a friend of mine always adds 10 % of oil sump capacity of diesel to his motors and fast idles them for about 20 minutes then drains the oil... his cam covers cams etc are always like new.
