Why is my 1991 Chevrolet camaro overheating(V6 engine)?
It doesn't smoke, tap or knock
I change the:water pump, thermostat, radiator, coolant sensors on the motor, catalytic converter
I got a radiator flush and transmission flush, oil change, fuel system cleaning, spark plugs and wires
I am not losing coolant and the fans are working

 

If it's overheating on the highway, look under the front of the car and make sure your air dam (spoiler looking thingy) is still hanging around. It's set back a ways from the nose of the car, and directs air up and through the radiator. If gone, that's the problem.

 

its not overheating on the highway (well the temp hand floats). Its begins to overheat when i first crank the car up. but i am missing the dam you're talking about.

 

Replace it. The air dam is a critical component of the cooling system. 3rd gens were built without grilles on the front, so the air dam is necessary to get air into the engine bay.

 

Your air dam isn't the problem. But get one back on anyway, it'll become a problem in extreme heat on the highway.
An engine overheating right when you start it up is impossible, even if there was no coolant in the block.
You have a gauge that's lying to you. Either the gauge, sending unit, or wiring is bad.
Have you checked your coolant level by the way, to make sure it isn't low, so that the sending unit can work properly?
The sending unit in the engine is designed to read coolant temperature, not air temperature.

 

This is a tough one let us know what you find out.

 

Well, its not overheating as soon as the car is turned on but its takes 15-25 minutes to start overheating.
-i changed the sending unit sensor
-A muffler shop told me that the manifold on the motor had rusty screws and was leaking and the manifold to egr valve was leaking also...Could that be the problem?

 

What temp is it reading? What do you consider overheating?