I have a 95 Z28 the guy I bought it from installed headers and placed plugs into the holes where the O2 sensor's were at. I bought the car test drove it and everything was fine I have had the car for 2 weeks and know it runs hot. All fluids are toped off and it sounds graet but now when Im about 30mph the temp is almost 250 degrees. what can I do. How can I fix it? thanks

 

Is the air dam still under the front bumper? If its missing it will overheat at MPH goes up, and air is not pushed up into the radiator.

Other thing to check is the fans. The fans should come on at low speed when the coolant reaches 226*F and go to high speed when the temp reaches 235*F. Is this happening? Do the fans come on at any temperature when you turn the A/C on?

Removing the O2 sensors is extremely unusual, and forces the PCM to run in open loop, eliminating its ability to fine tune the A/F ratio for optimal operating conditions (gas mileage and emissions). Are you sure they didn't simply plug the holes for the AIR pump connections, on the tops of the headers? In either case, it wouldn't affect the engine operating temperature.