Engine running hot

I have a caddy sedan. It was running hot so I put a new thermostat in it. While putting water in the radiator today while the car was running, water began leaking from the muffler and white steam coming from the tail pipe. What could cause that?

August 2008
Replaced water pump
February 2009
1)Message on dash - engine coolant hot, idle engine.
2) " " + - overheating, shut off.
3)Replaced radiator cap
4)Replaced thermostat
5)Replaced radiator
6)replaced coolant - problems begin !
With heater on -
Engine runs hot, dash messages return. Coolant backs up into reservoir, overflows - coolant withdraws into radiator. Bottom radiator hose cold, semi-hard has some pressure. Top hose hot, hard as rock. Hoses at tee hot, hard (top near firewall) - tee breaks coolant every where. Replaced tee, breaks again. Unemployed, money short - HELP !

New water pump/new thermostat/fans working properly car runs hot 15/20 miles down road I need what the problem to fix issue thanks

Okay I got a 1999 Cadillac DeVille it was running fine a couple days ago mind you that it only has 90,000 miles and rarely drive it sat for couple years but it's running hot out of nowhere so quit driving it changed thermostat changed water pump temp stayed at 196 for couple days ran it on highway was doing good then all a sudden temp jumped to 230-240° again after a week no leaks nowhere no white smoke out the exhaust but the overflow tank keeps emptying and it's saying low coolant and my change oil keeps coming on even changed the oil my gas mileage sucks big time it was at 8 gallons then when I left gas station it was at 4 already bubbling in overflow tank when it's hot I replaced the overflow cap too it feels like my water pump went out again after only being installed 3 days ago I'm thinking its the temp sensor I did hook it up to a machine at work and it says these codes any info would help I think it's the coolant temp sensor I reset codes and nothing has came back up the fans go on and the thermostat opens at 220 too because soon as it opens the overflow goes down and so does the temp and when I jump on highway it starts overheating when I drive backstreets or when it's raining out it won't overheat at all which is kinda weird idk I'm about to replace the coolant temp sensor next and the radiator just cause idk I won't give up until I figure out what it is lol