Checked the John Deere website and found plenty of declarations that their
antifreeze and coolant conditioner both are safe for aluminum.  Local Deere
dealer faxed me a sheet that, among other things, said, "Buffering control -
reduces corrosion of aluminum, solder, cast iron, and steel parts." and
"Cavitation protections - induces the formation of a very thin but tough
film on cast iron and aluminum surfaces to guard against pitting of the
liners and water pump impellers." and "Long life coolant specially developed
for heavy-duty diesel engines, plus it can be used in all gas engines with
aluminum blocks. . . . Coolant conditionser [the stuff that is equivalent to
Water Wetter but lower cost ] is part of the formulation [ of their ethylene
glycol antifreeze ] and is not required at initial fill."  Deere has a lab
that tests coolant and lets operators know if their "additives" are getting
low - if so, they add "conditioner" (the additives part of antifreeze) and
don't have to replace the expensive ethylene glycol, which is still good.
   -  There are 14 documents on their coolant and testing stuff.
   -  The initial John Deere website url is
http://jdparts.deere.com/servlet/com.deere.u90.jdparts.view.publicservlets.HomeUnsigned
then register and enter the site.  Then use the search item in left column
at top and enter part or product numbers:  TY16004 for "coolant conditioner"
(the additives package for renewing their antifreeze - or for use with water
if no anti-freeze is used).  Then, on the "search results" page, go down to
the blue Parts Information link to bring up the 14 documents.  The last
document takes you to the Coolant Eye (see next para)

While looking on the web site, stumbled onto this device:  TY16423, Coolant
Eye Valve.  It is a transparent plastic thing that goes in-line in a coolant
hose, and also has a pet cock for draining samples or for flushing, etc.
   -Lets you see the coolant at is circulates.  Local dealer has one - it
is clear hard plastic.  Package says "Keep away from turbochargers and
exhaust heat." If I had it in an airplane, I'd put "fire sleeve" on it.
   -  Might be useful in early testing phase to check for bubbles, etc. -
or for "any flow at all".  Maybe consider as an "engineering development"
tool.

David