Civic doesn't warm up.

[green91]

Go ahead and replace the thermostat first. If your engine isnt reaching operating temp the ecu is going to stay in open loop which enriches the AFR, meaning you're gonna get worse fuel economy than if it were in closed loop.

[Derek2]

i bet you cross threaded the cheap plastic fine threaded drain plug, go buy a new one and try again....why the hell did you drain all the coolant for a thermostat anyway????