Chevrolet Repair Questions? Ask a Mechanic for Answers ASAP
I'm not sure the sensor or the wiring are bad if the engine is running hot. All of the work that you've had done have all been seperate issues, but they may have aggravated an underlying issue of a failing head gasket. If the temp is going high like that since the water pump and the flush were performed, there is a good chance the tech that replaced the pump and did the flush did not bleed the air out of the system correctly. There is a specific fill procedure for this engine, and if it is not followed, overheating and engine damage can result.
With the engine off, and the radiator cap off, open the bleeder screws, one at the bypass pipe above the water pump and one at the upper hose outlet on the driver's side front corner of the engine where the upper hose connects. Fill the cooling system with a 50/50 mix of Dexcool and water until just coolant and water come out of the bleeders, NO AIR. Close the bleeders and top off the coolant.
If you got alot of air, or if it continues to overheat, you may have a head gasket failing that is allowing combustion gasses into the coolant which prevents proper coolant flow.
If you take it to a shop, have them perform a combustion gas analysis on the cooling system. This will be a clear chambered tool with a squeeze ball on one end. The tech will fill the cylinder partially with a blue "Test fluid" that will turn yellow if there is combustion gas present in the coolant. This will verify my suspicions.
Depending on how long you drove the car with low coolant prior to any of the previous repairs may have started this chain reaction, but I don't want to speculate. I just want you to understand what could be going on.
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I don't think he's going down the right path. The sensor that he is reffering to is the ECT or Engine Coolant Temp sensor. This sensor responsible for telling the computer how hot the engine coolant is AND to let the Instrument cluster know how how hot the engine coolant is. If the gauge is working, then the computer is getting the signal. If the fan is not coming on, there could be a problem with the fan or the relay.
Does the service engine soon lamp some on? If so, did he tell you which code has set? This might help me understand where he's coming from.