coolant flushes

[Brett Dikeman]

So by accident in the course of investigating coolants, I discovered
that Mercedes-Benz strongly encourages coolant flushes, and pretty
extensive ones at that.  Apparently the common procedure is to pour in
a 1:2 or 1:3 mixture of Shout (because it is low suds) and water to
degrease/deoil, and then after that has been flushed, citric acid is
added to remove corrosion and rust, if any.  Someone commented that
citric acid makes for a good metal corrosion remover, attacking
corrosion but not doing much to the base metal.

  You can buy citric acid from the Merc parts counter in half-kilogram
packages, or online from various food-related sites.  Some of the
coolant flushes available in your FLAPS may contain citric acid,
though it sounds like sodium somethingorother has been substituted in
many of them.  I read one post by a chemistry nut which said that
alkali flushes are good for removing deposits left by coolants, and
acid ones for removing corrosion.

It was stressed that without the de-oil/degrease step, the citric acid
step is worthless.

Read up on it yourself, but the only caution I saw was not to run the
engine for long periods of time on the soap or the citric acid, as
there are no lubricants to keep the water pump happy.  Sounded like
most people run the stuff until the engine gets up to full
temperature, then flush extensively.

I was also surprised at the steps required to bleed BMW and Mercedes
engines of air- all sorts of talk of varying throttle levels,
squishing hoses, removing bleed air screws...if memory serves, the
Bentley for the 200q20v doesn't say much except to put the heater on,
park on an incline, and run without the cap on for a while.  Is there
in fact a better way?

Brett