Fat?

[Jeff and Stash Blackwood <ichindar@magic1.org>]

I am working on a 59 Magnette that had been sitting for a number of 
years. When I pulled the thermostat housing, I found the neck of the 
housing to be full of a fatty substance that varied in color from 
brownish-white to fluorescent green. Any ideas on what it was and how to 
clean it from my system? By the way, it doesn't run, so taking it to a 
radiator shop to have them boil it out is out of the question.

Thanks.