ENGINE TEMP GAUGE READ 3/4. 235 DEGREES PER SCAN TOOL. REPLACED THERMOSTAT AND FLUSHED SYSTEM. PROBLEM THE SAME CLUTCH FAN SEEMS OK.

Smart man using a scanner for the actual temp. Assuming you're not losing coolant....2 things I'd look at here, 1st is you may have air in the system, make sure to purge all the air. 2nd is your fan clutch, I've replaced a few fan clutches in my own Trailblazer. Have had them bad right out of the box brand new. Have had bad brand new fan clutches on 2 of my last Trailblazers. You should hear it engaging especially in stop and go traffic.

It mite not be running hot at all , I replaced a few stepper motors for the temp. gauge inside the instrument cluster . GM products of your year ,have known instrument cluster gauge problems . Best thing is to hook up to a factory scan tool or another type of professional grade scan tool to see what the engine computer is seeing from coolant temp.sensor Do your cooling fans come on ? They should at about 221 degrees . Or you came go to harbor freight an by a temp. inferred gun. point it at the upper radiator hose near the thermostat , an see what the actual temp. is . How to repair GM Instrument Cluster Speedometer Gauge Stepper

If you replaced the SENSOR and not the gauge SENDER, there's your answer.

The SENSOR sends the computer (ECM, PCM, ECU, etc.) the engine temp so it can make the adjustments to the fuel, timing etc.

The gauge SENDER makes the gauge read what temperature the engine coolant is.

Hope the helps.

Try a new temp sensor.

I'll put my bets on a faulty gage...but that's just me.

Have you checked your cooling fan to see if it is working propely? Let the car idle and get warm and listen for the fan to kick in (if they are electric) or just watch to see if the fan starts to spin faster if it is the old school type with a clutch. Have you replaced the thermostat? A bad one will let the temp rise since it opens too late and then the temp will drop off. But it won't due this only at a light and it will do it infrequently.

fans came late on those car,like 212 and second fan comes on at 224,you reprogram it to come a lot sooner,,other thing is there might be gunk inside the block,and coolant has hard time to pass through,and staying longer than enough in block temp goes high,even tough the radiator is doing it's job,it is just coming out block lot hotter than it suppose to be,and gauge read the block not the radiator

The first hing I would do is confirm the engine temp with a scan tool. If the scan tool is reading a normal temp, 200 to 220 degrees with the fan coming on at around 220 degreese, and the gauge us reading much higher than the gauge is most likely bad. If the fans are not coming on than you need to look into that. Fuses, relays, wiring, fan motors would be the basic things to check. If you need more help with figuring out the fans let me know. If the fans are coming on, the temp gauge is reading the same as the scan tool data that there are a couple of possibilities. Either the system has air in it from nepot being properly bled or the headgket is bad forcing air into the system. Air will cause the cooling system to lock up. If you are try ing seeing the temp gauge spike to 260 degreese the head gasket is likely to have or will fail soon. Like I said if you have any further questions let me know and I'll be happy to help.

I’m happy to assist further over the phone at https://www.6ya.com/expert/jeremy_d728a59f986299fa

Did the engine overheat before the water pump was replaced? If so, you may have a warped cylinder head and/or blown head gasket.

Was the radiator full of rusty-colored liquid before you flushed it? If so, your radiator is probably restricted with rust deposits in the cooling tubes. Flushing WILL NOT get this stuff out. The radiator MUST be replaced if this is the case. Your heater core is probably not in real good shape either, so you should be expecting some heating problems this winter.

If the above is not the correct answer, then you should check to make sure the temperature gauge is not "LYING" to you. This could be caused by a defective gauge, a bad temperature sending unit, or faulty wiring.

The way to check this is with a scan tool that can read engine data and an infrared thermometer. While reading the coolant temperature data from the computer, check the cylinder head temperature with the infrared thermomometer. The readings you get should be within 5 degrees (F) of each other. If the computer data does not match the thermometer within the 5 degrees, then the sending unit for the computer should be replaced.

Then look at the gauge to see if the gauge reading is appropriate to the temperature readings that you took. Normal operating temperature is between 190 and 230 degrees. This should place the gauge at slightly to the right of center to about 5/8ths of the way to HOT. If the readings you took are OK and the gauge is reading higher than this, then you should try replacing the temperature sending unit for the gauge and see if that fixes the problem.

Please note that there are TWO temp sending units: One for the gauge and one for the computer.

You may have been given the wrong thermostat. Either way, you can try a hotter thermostat. If the water pump has never been changed it might be time for a new one. I've already had one that was so old that the propeller inside had the fins rusted completely off and the bearings were so bad it was messing up the timing of the motor. The truck wouldn't idle. And guess where alll the rusted off propeller chunks ended up. . . that's right. In the radiator, heater core and the thermostat. I flushed that truck for three days in both directions to get all that scrap out of there. Good Luck. And if you still have the old thermostat you can always throw that one back in, just to see what happens.