My 2002 civic sedan overheats when i turn on the ac and or heat. It seems that once I put on the fan the system starts losing coolant and will eventually overheat. My passenger side floor becomes wet when this happens which makes me believe that I have a small heater core leak. Can anyone confirm that this is a tell tale sign?

With that being said, should I take it in to a local mechanic to get the heater core replaced? I want to use Stop Leak but after hearing the horror stories I want to know if its worth the risk or if there was a way to only isolate the stop leak to just the heater core. Any ideas?

I don't want to get rid of the civic because the motor and trans are solid but also cant justify spending almost a grand on the car.

Thanks!

 

A heater core leak should be consistent... not just when you have the A/C or heat running. Also, you would have to be constantly filling the radiator from what is leaking into the floor board. The liquid may in fact be condensation from the condenser that isn't getting out of the car. It is common that the hose leading from the bottom of condenser housing gets detached and thus the condensation drips on to the carpet. If the fluid isn't colored green or blue and it doesn't smell like anti-freeze, it is likely just water and thus the condensation that I have stated above.

Do NOT use stop leak in your cooling system.

The overheating may be a separate issue... unless you are low on coolant. Check the obvious things first: Bad radiator cap, thermostat problems, low coolant level, and electric fans failing to come on would be where I would start.

 

A shop is going to charge a pretty penny to do a heater core. The dashboard has to be pulled out as well as dropping the steering column etc.

You should smell coolant in the cab when the passenger floor gets wet. But yes usually the wetness on a dry day is indicative of a leaking heater core.