ken 270,
This is my understanding. Just being a multi-grade oil does not necessarily mean it will have a higher detergent rating than a single grade.
There should be no problem using a multi-grade oil in an old engine.
Modern engines are manufactured with tighter tolerances, higher operating temperatures and are mandated to achieve better MPG.
The multi-grade oils were 'invented' to answer all of these requirements.
The early engine simply does not require the more expensive $$$ multi-grade oils.
It is my understanding that the "detergent" in a motor oil will not actually scrub the inside of a dirty old engine. The true purpose of a detergent is to hold dirt, acids and gunk in suspension until they can be drained with the oil during a change.
I have seen posts stating that switching to a detergent oil will plug the oil filter with all this suspended glop.
That's my take on your questions!
Stuart
