Paul wrote:

This is some crude accumulated in the top of the water
jacket partially blocking the flow of coolant. Needless to say
you would not want this stuff in the water jacket near the spark
plugs. Crude obviously rises with coolant bubbles.
This engine was overhauled about 2 years ago so I expect
the coolant was not changed in that time period.

Bill Freeman replied:

This fits with my suspicion of the engine sitting for a while
with a low coolant level.  The crud forms at the surface where
the air is available for corrosion and to oxidize 'stuff' into
'crud'.

Russell Kent wrote:

Well, ignoring for the moment the tempting target Paul's misspelling
makes ("crude" instead of "crud"), I'd like to point out that the air
bubble in the cooling jacket isn't an infinite supply of oxygen.  As the
air's oxygen is used to oxidize the "stuff" to make crud, there's less
oxygen available.  So the question is, is there enough oxygen in the
small trapped air bubble to make all of that crud?  My gut reaction is
"no," which means that there is something else going on in addition to
any oxidizing action.

Russell Kent

Sorry about the mis-speeling Russell. I hope it does not keep you awake tonight :-)

Water is H2O. Perhaps by heating it, oxygen and hydrogen  is liberated. 
True, the pressure is increased greatly but that is vented off by the 
radiator cap. There may also be dissolved gases in antifreeze.

When you boil water in a pot on the stove little bubbles mysteriously appear
at the bottom of the pot next to the hot surface. How did that gas get
down there in the first place? 

Paul Lamar
 
The Aircraft Rotary Engine Newsletter.              Powered by Linux.

http://home.earthlink.net/~rotaryeng/            http://www.linux.org