I changed the radiator today and drove to work, same thing: overheating and boiling. Don't see a leak from the radiator or anywhere else. The thermostat was changed and still no change. I am stuck, so I need advice. The plug to put the diagnosis machine on under the dash seems to not read. I know it works but no codes even come up. What might be going on with the cooling system?
Next test steps are:
Test for proper fan operation. The fan should come on when the A/C is selected on regardless of coolant temperature, this is a easy way to ensure that the fan works. The fan should come on when the coolant temperature exceeds 200 Deg F and run for around 20 seconds. The run time depends on ambient air temperature and humidity. Fan on time should be less than 1/3 of fan off time. A short fan on ratio indicates good heat transfer in the radiator. Test radiator temperature: It should get hot, over 190 deg F.
Test for a failed head gasket, a common problem on some years of Civics. This is generally considered a test best done by an experienced diagnostician. If one gets all the air purged from the system and more keeps coming the head gasket is likely the cause of the problem.
It can be helpful to use the diagnostic plug and a scan tool to check the system temperature but it is not required. Trouble codes are not provided for overheat problems specifically. A temperature sensor over limit code can set but this does not tell us anything we did not already know.