HouseCallAuto 10/8/2012Measure the two heater core hoses at normal operating temperature. With full heat commanded and blower motor on High, I would expect to see roughly a 20-30 degree difference between the hoses. An extremely large difference (60 degrees or so) would indicate a completely plugged heater core that is not allowing flow. A small difference (5 degrees or so) would indicate a partially restricted heater core that is only allowing coolant to flow through a small portion.
The answer to that will get me to the next suggestion. Cannot cover all possibilities in one post, sorry.