1996 buick roadmaster keeps overheating: already replaced the thermostat, water pump, heater core, heater control valve, hoses and anti-freeze

you may have a air pocket and it needs to be bleed. check and see if both heater core hoses are getting hot

Check for the following causes:

• Insufficient coolant - i. e., not enough to permit flow in the heater core.
  
• Anti-freeze concentration (too much water will allow the liquid to freeze in the radiator, heater core or hoses). This can also cause engine overheating.
• Collapsed hose to heater core (check both hoses).
  
• Bad thermostat on engine.
• Heater blower not working.
• Heater door not opening.
  

WATER PUMP FAILURE COULD BE CAUSED BY WRONG COOLANT USE DEX COOL ANTI FREEZE.REPLACE THERMOSTAT AND BOTH RADIATOR HOSES TOP HOSE AND BOTTOM HOSE.SOFT HOSES COLAPSE LIKE PUMP HOSE.IT WILL COLAPSE FROM PUMP VACUUM CLOSING OFF SOME COOLANT FLOW.MAKE THE HEATER CORE NOT STOPPED UP IF SO IT WILL RESTRICT WATER PUMP BYPASS CAUSE EARLY PUMP FAILURE.YOU NEED 50/50 COOLANT MIXTURE YOU HALF WATER AND HALF DEX COOL DONT USE GREEN ANTI FREEZE USE ORANGE DEX COOL.I HAVE 3.4L ENGINE AND 3.1L ENGINE BEEN USING DEX COOL ANTI FREEZE SINCE I HAD BOTH VECHICLES. HAD NO WATER PUMP PROBLEMS.

Bad heater core. Replace it.

good day, heater core/coil is leaking antifreeze and needs to be replaced. The heater core works in conjunction with your engine's cooling system. The function of the cooling system is to remove heat from the engine, and it does this for the most part by sending the heated anti-freeze to the radiator located in the front of the car. The position of the radiator allows outside air to blow across the radiator thus cooling the anti-freeze. The anti-freeze is then sent back to the engine. Hot anti-freeze is circulated throughout the cooling system by the radiator and heater hoses. Think of the heater core as a small radiator located inside the dashboard of your vehicle. hope this helps, have a nice day.

If you have the Auto temp control; and you have checked the coolant level then you may need to replace the module that is under the dashboard on the right side footwell,. this is a common problem on these cars. When you remove the plastic under dash panel, look up and there is a module in the duct for the heat that determines the temp so the Climate control works correctly. I pulled mine out of a junkyard car and saved about 80 bucks.

check for proper ratio of anti freeze and water, check belts, 

you probably have a bad thermostat which caused the overheating in the first place which popped the hose off

THE STOP LEAK MAY HAVE PLUGGED YOU HEATER CORE TUBES, BUT AT THE SAME TIME CHECK THE HEATER CONTROL VALVE. IT MAY BE RUSTED OR CORRODED AND INOPERABLE. IT WILL BE LOCATED ON ONE OF THE TWO HOSES THAT RUN TO YOUR HEATER. I WOULD START WITH THE HEATER CONTROL VALVE. GOOD LUCK.

Check your coolant level first. Next check your heater control valve. With engine at operating temp and heater on high, do this:

1. Heater hose from water pump should be hot (if not, water pump may be dead or thermostat is stuck closed)
2. Heater hose from thermostat housing should be hot (if not, thermostat may be stuck closed or water pump is dead)
3. Heater hose going to heater core should be hot ( if not, heater control valve is not getting vacuum from heater control unit, or valve is broken)
4. Heater hose returning from heater core should be hot (if not, heater core is blocked, undo both hoses to core and flush with water hose until clear)

Test thermostat: with cold engine cranked, watch water temp gauge. As it gets hotter and hotter, when the thermostat opens, the temp should drop suddenly and then go back up.

Test water pump: with engine at operating temp. Squeeze top radiator hose tight, when you release it, you should feel/hear a surge of water. It is much like when you pinch a water hose closed and release it.

Test vacuum from heater control unit to heater control valve: undue vacuum line from control valve. It should have a vacuum when pressed against you skin in addition to releasing the actuating arm on the control valve.

If there is no vacuum, a quick fix will be to disconnect the plastic actuator from the silver arm on the heater valve. This will let the hot water to always flow to your heater core.