2) You might have an air lock. You may have to help the air out by massaging the hoses while leaving the cap open (with the engine running). And it might help if you leave the cap loose (so air can leave the system easier) while driving for the next day or two. Leave a bottle of 50/50 coolant in the trunk for the next few days to refill the tank.
Did you retrieve all the pieces for the water pump (if it broke into pieces)?
1) Check the ECT gauge sender unit. It is the "bronze" sensor under "Co" in the word coolant in this picture. Per Haynes, if temp. gauge in dash reads hot after engine is started from cold, disconnect sender�s electronic connectors. If the gauge reading drops, replace sender. If the gauge remains high, there may be a short in the wire to the gauge. Sometimes overheating will break the sender unit.
Additional test from Autozone.
http://www.autozone.com/servlet/UiBroker?ForwardPage=/az/cds/en_us/0900823d/80/1b/c3/79/0900823d801bc379.jsp
