Quoting eight-time Automotive Journalism conference MOTO award winner 
Robert Sikorsky's, Drive It Forever, page 83.
  "Another reason for keeping the oil "full" and never --but NEVER-- 
allowing it to get below the "add" mark is that about 40 percent of the 
engine is directly dependent upon the oil to cool it.  Oil must act as a 
coolant for such vital parts as  the bearings, crankshaft, and timing 
gears; in fact most of the lower engine depends upon a constant supply of 
circulating oil to cool it.  The more oil in the crankcase, the better 
its ability to remove heat.  In a small engine, the cooling capacity is 
increased by 33 pecent and in a large one by about 20 percent by keeping 
the oil above the add mark.  This point becomes more critical when hot 
outside temperatures demand additional cooling from the oil.  Oil is a 
vital cooling fluid -- keep it topped off for maximum engine protection." 
  Lots of SAE Journal citings support the vital importance of oil as the 
second engine coolant.  If someome successfully confutes SAE Journal 
contributors on this issue, I'll soon be citing them, but for now, I'll 
stay with the lab test data supported view.
	Cheers,
	John Wakefield