Heh. I was going to start this thread myself this morning, but can't say I'm surprised someone beat me to it. Over the weekend, we had an arctic system move through the Montana area, bringing lows to -23F at my house. Thankfully, the heater was cranking through that period, and I thought was doing so fairly well. One the way to work this morning (mid-20s) it didn't seem to be getting any warmer, and I discovered that it was blowing pure cool air.
I know it isn't the water pump, as that was replaced by me a few months ago when the seal failed. It runs at the normal operating temps, and heats up to it in a typical amount of time, so at least I can rule that out. The coolant is good, being only as old as the water pump (70% of it was replaced, only a portion was recycled, and the radiator is <1 year old and was replaced not long before I got it.
Now, I'll try flushing it this weekend to check for blockage, but if this fails, how much work is required to make the core accessible in order to clean the fins or change it out? This is a poor comparison, but when my buddy replaced the core in his Taurus, he had to completely disassemble the entire dash to get to it.
Also, would the likelihood be more that the flap thing mentioned might not have something to do with it. I have noticed quite a bit of cold air coming in there, and seems to be sticking a bit. I have trouble getting the airflow completely to 'off', and it wants to stick on heat, more than anything. I'll run out at lunch and take a look, but any other input would be appreciated. I'd like to know now if I get to spend Sunday bent over the fender ripping the back half of the engine apart.