I have often bragged that I have rebuilt almost everything on a 240, that I have delved into the deepest depths of the car and come out alive. The truth is, I have thus far escaped the one job I dread more than any other: replacing a heater core.

In the past few months, I began to notice that it was very difficult to defrost my windshield. I also noticed a very slow drop in the coolant level. It wasn't until a warmer day, upon which I still found little half-circles of vapor on my windshield, that I realized there was trouble.

Having a second 240, I decided to park my beloved black sedan until it was warm enough outside to tear apart the interior. Now, my wagon has a failing and irritating transmission, so I guess I better get one car into good shape.

Before I buy a heater core and disassemble my car until it looks like a Build-Your-Own-Volvo kit, how can I be certain that that is the culprit? Just check the A/C drain and heater valve? Anything else possible?

Thanks,
Sean