Cooling system question

["Louis A. Mulieri" <lmulieri@zoo.uvm.edu>]

	Nothing like a long trip to generate questions about my car.  I 
bought this car last September and have no experience with driving it 
in hot weather.  On this trip we had some warm weather, mid 70ies.  The 
temperature guage would climb to slightly above half way as I climbed a 
long, (2-4 mile) hill at high speed, 70-80mph and would then fall to 
slightly above one quarter as I descended.  Given all the feed back 
control in this car I am surprised at this variation in engine 
temperature and wonder if it indicates some incipient cooling system 
failure or does it mean that the cooling system has just barely enough 
capacity for heat dissipation so that a little stress overwhelms the 
control mechanisms.  	
	Another question.  Given this behavior I was hesitant to use the 
a/c as I thought this would exaccerbate the problem but in fact with the 
a/c on the engine temperature ran lower and was more steady--I don/t 
understand this; does anyone have an answer.
	
	TIA

	Berthann Mulieri