I have found over the years, that Marvel Mystery Oil is the best to keep
the inside of your engine clean when used on a regular basis.
It will keep your rings free, and keep varnish, and sludge from forming
inside your engine.
However, if you have a high mile engine, and regular maintenance hasen't
been the norm, it may cause seal or gasket leakage, when you start
cleaning up all the garbage that`s holding your engine together.
I have been using Marvel for 30 years,
and have found it to be a superior product.
I even put it in my gas for a upper-end lubricant especially when going
on long trips (Really is good for the Vanagon)
Happy engine cleaning,
Terry
85 GL