I have a '98 Accord sedan, 4 cyl, auto with 127k miles, and just recently like within the past week or so, I'm barely getting any heat in the car. Up until then, the heat used to be nice and hot but now it's barely warm. Not the best thing considering the outside temps been dipping into the teens in NJ!

I'm thinking that my heater core might be the culprit here, either the unit or that it's clogged up or something. My thermostat is fine because the car warms up normally as it has always; the coolant level is good including the reservoir; the water pump is practically new as it was changed recently with the timing belt.

I was thinking that if the heater core is dirty/clogged up, maybe I should start off with flushing out the entire coolant system, which should clean out the heater core as well. If that doesn't work, then go from there, like maybe replace the heater core itself, etc.

So does any have any ideas as to what it can be or how to troubleshoot it?