I found this in the archives, thought it might be interesting. Jim

Many of the older, better-known oil treatments on the market do
not make claims nearly so lavish as the new upstarts. Old standbys
like Bardahl, Rislone and Marvel Mystery Oil, instead offer things
like "quieter lifters," "reduced oil burning" and a "cleaner
engine."

Most of these products are made up of solvents and detergents
designed to dissolve sludge and carbon deposits inside your engine
so they can be flushed or burned out. Wynn's Friction Proofing
Oil, for example, is 83 percent kerosene. Other brands use
naphthalene, xylene, acetone and isopropanol. Usually, these
ingredients will be found in a base of standard mineral oil.

In general, these products are designed to do just the opposite of
what the PTFE and zinc phosphate additives claim to do. Instead of
leaving behind a "coating" or a "plating" on your engine surfaces,
they are designed to strip away such things.

All of these products will strip sludge and deposits out and clean
up your engine, particularly if it is an older, abused one. The
problem is, unless you have some way of determining just how much
is needed to remove your deposits without going any further, such
solvents also can strip away the boundary lubrication layer
provided by your oil. Overuse of solvents is an easy trap to fall
into, and one which can promote harmful metal-to-metal contact
within your engine.

As a general rule of thumb these products had their place and were
at least moderately useful on older automobile and motorcycle
engines of the Fifties and Sixties, but are basically unneeded on
the more efficient engine designs of the past two decades.

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