What would cause a faint smell of antifreeze coming through the vents when the heater or AC is on? It's much stronger when the unit is on low speed than when it is on high. It has lessened in the past week or so and isn't quite as bad. When it first started, I got in one morning and when I turned the heat on the windshield fogged over and eventually cleared at the bottom where the defrost vents are but not from the middle up. I would really appreciate any thoughts on this.

 

sounds like a leaking heater core

FordMasterTech

 

We took the truck to the dealer and they said they couldn't find any leaks with the heater core. They told me that I had sediment/build up in the radiator and the engine block that was causing the odor. They wanted $400 to flush the system. Would a flush kit from Auto Zone work about as well or would it make it worse if there really was a leak in the heater core? What should I run through the system to take the odor from the vents?