Cooling system

The temperature sensor may be inaccurate. You can determine this by using a scan tool to read the sensor temperature.

I replaced the temperature sensor with new one's and used a scan tool to read the sensor temperature. The reading is the same i.E Red lamp on at 94 degree c instead of 120 degree c.

I did not advise you to change anything. I advised you to read the temperature using a scan tool.

I have a Hyundai new accent 2008 car, 1.6 l, 4cyl, fwd, manual 1.6l, 135000 km,
Because of overheating before, an over hole maintenance was taken and due to a little deformation in cylinder head, 2 head gasket are installed to compensate the cylinder head thickness after resurface it
The cooling system have 2 indicator lamps one blue for low temp. And the other red for high temp. After some weeks I found the red lamp on in traffic but didn t in highways
By checking the cooling system
Replacing thermostat, temperature sensor, radiator cap,
Cleaning radiator (aluminum type) internally and externally, checking the coolant level regularly is detect no leaks
Checking the electric fans operation are ok.
Checking water pump impeller is ok.
Checking by using another controller
Checking by using instrument cluster and indicator lights panel controller
Checking bad gasket and cracked head using block tester and test fluid it found ok.
After that I found the same state red lamp on in traffic but didn t in highways
Using scan tool which indicate that red lamp is on at 94-96 degree c and radiator fan on at 96-98 degree c and code p0118 ( mean engine coolant temp. Circuit high input) so why red lamp

Because you have a problem with the coolant temp sensor circuit. You will have to have the circuit troubleshooted to resolve the P0118.