I have a 1998 civic and even though i've replaced the water pump, thermostat, temp sensor, fan switch, fan relay, basically everything but the radiator but water flows through fine so i know it's not that. any help would be appreciated guys!!

 

Gonna need more info about what it's doing then that... Tiny bubbles in the coolant? White exhaust smoke?

 

head gasket?

 

does it "push" coolant out the overflow? Is there pressure in the radiator that blows out when you open the cap when the car is cold? Those are common signs of a blown headgasket or lifting head.

 

put a block tester on it so we can rule out a bad head gasket if it reads good. or we can say its the head gasket thats bad if it reads bad. we're guessin here because we only have what you posted to go off of. do the block test and let us know

 

Can you explain because I've never heard of this one... There should be pressure in the radiator because the cooling system builds pressure. Pressure in the system means your rad. cap is doing its job.

 

Any more details about your set-up? Stock?

What kind of Tstat did you buy?

Check this link out:
Overheating Troubleshooting Guide

 

air in ur system>?