Overheating 99 pontiac grand am

Are getting all the air bled out of the cooling system?

How hot does it get in degrees F? Does the radiator fan work? Some fans won't turn on till about 220 degrees F.
Could have blockage in radiator or engine block? Check the water pump. Your serpentine belt ok? Could be gasket issues? Any coolant in the oil or oil in the coolant. Check your coolant temp sensor. Don't replace anything unless your testing points in that direction. Are you losing coolant?

Head gasket ? What engine ? 3.1 l v-6 ? Coolant in the oil ?

u should check for a faulty thermostat first, they are only a few quid and easily replaced. if no change ur most likely faults are a blocked radiator or faulty water pump. u dont sayhow old ur van is but after the thermostat go to the radiator, when its hot check the bottom of the rad to make sure its hot, also brown water means u need to bback flush ur cooling system. even tho u have changed some sensors doesnt mean u got the fan switch sender, dash board sender and fan sender tend to be different sensors, so just double check.

maybe a water pump.

try priming the engine block & radiator with water though the hose's & any hose you can squeeze to pump out the air lock with the filler cap off when running, sounds too much air is is in the system & the pump won't work dry.
I had this problem a few times & I ended up practically forcing water into any hose I could re-attach quickly using a garden hose, as the heating system need's priming too !

I had trouble with overheating on my 2000 Grand Am, The dealer could not even resolve the issue,(they wanted to replace the intake gaskets)...I knew that was not the issue, no air leaks or water leaking there; so I sit down to think; what are the causes of overheating. Thermostat sticking - nope not it, water circulates, Water leak - nope not it, has water stays until it gets too hot and goes out overflow, fans working - yep...hummmm the only other thing I could think of was losing of water pressure, yep that's it - the cap on the coolant tank was going bad, got a new cap ($8.00) replaced the old one and no more trouble going on 6 months now.

Hope this may solve your issue.

That leaves radiator or radiator fan problem or wrong thermostat. Did you or a mechanically inclined friend do the repairs ?

1 Inspect Cooling System Mix Coolant level low or flow is restricted. 2 Inspect Belt Incorrectly routed, adjusted, tensioned, missing, or worn water pump belt(s). 3 Inspect Oil Pan Gasket - Performance Ruptured, cracked or leaking radiator hose. 4 Inspect Radiator Cap Worn or damaged radiator cap 5 Inspect Thermostat Thermostat stuck closed 6 Inspect Fan Blade Broken, missing, or defective fan blade(s). 8 Inspect Water Pump Damaged, worn or leaking water pump. 9 Inspect Intake Manifold Plenum - Perform Leaking water pump gasket. 10 Inspect Cooling Fan Control Faulty cooling fan control or circuit. 11 Inspect Cooling Fan Switch - Radiator Faulty radiator cooling fan switch or circuit. 12 Inspect Engine Temperature Sensor Faulty engine temperature sensor or circuit. 13 Inspect Temperature Switch Damaged or faulty temperature switch or temperature switch circuit. 14 Inspect Fan Clutch Worn, loose or faulty fan clutch. 15 Inspect Ported Vacuum Switch Damaged, leaking, or faulty ported vacuum switch. 16 Inspect Radiator Obstructed radiator core or radiator cooling fins. 17 Inspect Head Gasket - Performance Head gasket leaking coolant into cylinders

i dont think it needs a waterpump. what temperature thermostat did you put in? unless the fan is running all the time maybe. i would try another thermostat, the engine needs to be at least 195 degrees to produce decent heat.