My trailblazer keeps overheating and I'm not sure why. I have already replaced the radiator, water pump, thermostat, and clutch fan. Is there anything else I can do?

CJ, this is very common for the I6 engines in TB's and Envoys. You need a new fan clutch. Triple check the wire connectors first, located on the top of the radiator on the drivers side, make sure those are in tact first. Then replace the fan clutch. Might as well do your water pump and serpentine belt while you're in there.

Your cooling fan relay is bad.

Sounds like the water pump fins aren't doing their job. I suggest changing the water pump. Been there, done that. Bad pump.

If the coolant pulls down with the radiator cap off when increase engine RPMs the water pump is OK.These vehicles had been known for cylinder sleeve problems and head gasket problems.

Is the water pump leaking coolant? If not, then why do you think it's bad?

If the engine is overheating, there are several other things to look at before you consider the replacing the water pump.

Are the fans electric motor driven, or fan belt driven? If fan belt driven, replace the fan clutch. If electric motor driven, check the fan control module and/or fan motors to make sure all is good there. Fan control module tend to fail in weird ways, so if nothing is wrong with the motors, replace the module.

Always, always, replace a thermostat that has overheated. Once overheated, they consistently fail. Make sure you properly refill the radiator with coolant after the stat is changed.

Check that the bottom radiator hose does not collapse.

Check the radiator for corrosion. Boil the radiator out, or have it done, or replace the radiator.

I have a 2004 trailblazer and it keeps over heating at stop lights or while driving slow. I have replaced the thermostat and water pump, but this issue still shows up. It is fine while driving down the highway at 55-65 mph. I have also cleaned the radiator and blew through the fins to clean out the dirt and bugs. Not sure if clutch is operating correctly. How can one tell if it is and are these electric? I know there are approx 5 wires running to the front of the clutch, but not sure if this gets a voltage signal to engage the clutch fan. Any ideas?

overheating has a few possibilities.
thermostat.
low volume from water pump.
air lock caused by a small leak
cooling fan not coming on. from radiator fan switch or relays.

have the system pressure tested,
check the fan operation,electric or clutch fan.

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

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1. start the engine and leave the radiator cap open.
2. put a cardboard cover or a rug in the front of you radiator.
3. let it runs 20 minutes or more, see if it is overheated and see the water or coolant in the radiator circulated or not. If not, as soon as you have already changed water pump. thermostate and check the hoses, no leak, I think your radiator was blocked.

Did you put stop leak before?