heater core?

where is the heater core on a 1990 escort Lx?...easy to replace?

the job calls for four hours it took me six&half hours and its still biting me in the ass

My heater core was leaking and I put some Aluma seal in the radiator. It stopped the leak and isn't clogging up my radiator. I would try this first before pulling the heater core which sounds like a bear of job to me.