Using this stuff can be very dangerous for your engine. If your engine
is that dirty inside it is due to neglect. If there is a heavy buildup
of carbon or sludge, these solvents will cause them to loosen. The crud
in the bearing passages will soon move into the bearings causing damage
there. The crud sitting in the heads and oil returns will loosen and
eventually accumulate and clog the oil pump inlet screen. The heavy
carbon can not be dissolved by any solvent so you are now stuck with no
oil pressure. In the Water boxer, the only way to access the oil pump
screen is to completely tear down the engine. The air cooled busses have
removable screens so this is not as much of a problem. Most other cars
can have the pan dropped allowing oil pump access there.

Questions to be asked include why do you think you need to flush an
engine? If it is running okay, it obviously is not necessary. Remove the
valve covers. Is there a load of carbon and sludge on top of the heads?
Are the deposits flaky or chunky? If yes, simply loosening them up will
be devastating. I've seen engines with so much crap on top, there were
imprints in the crud where the rockers moved. If this is the case, Then
carefully remove as much junk as possible by hand. A shop vacuum can be
used to suck some of it out. If the engine has a removable oil pan, then
remove it and clean all the open passages out. Remove and clean the oil
pump screen if needed. On the Water boxer, remove the rockers and
pushrods to clean out the tubes if needed. Again, be careful not to let
the loose crud go down into the crank case.

The best way to clean an engine is to just do frequent oil and filter
changes. If the engine is healthy, this is all that is needed.
Synthetics tend to clean better and since they do not break down, they
will not add any more crud in the future. I do not believe in adding oil
additives or Marvel Mystery oil. Good quality oil will do everything
needed. Modern synthetics have proven their value to me over the years.
Make sure to use the proper viscosity. If your engine is tired, cleaning
with a solvent will not fix it. Save your money.

Dennis