Hey guys: Ford fan, new to this forum. Have an '09 Expedition I just got, 65k on it. First time I used heater - getting strong exhaust-like fumes, kind of like a combination of exhaust and that smell you get when you turn on an electric heater that's been collecting dust. Making me ill. This is definitely not a typical core leak - no antifreeze smell, which I know well, nor any coolant on the ground. When the a/c is on no odor at all. Does the fan take external air from different places? How could exhaust - or any engine smell - get into the heater core box? Same smell from the back unit - which is even stranger. I don't want to change the core/s unless I now it will likely fix it. This s**t makes me crazy. Any feedback would be appreciated.