I had this problem in my turbo truck. As it turns out, the PO was dumping Bars leaks in it regularly atempting to fix a crack on the top rad tank. All that did was clog the heater core. I first tried the garden hose and found that the core was severely cloged and flowed very little. Some stuff that looked like urathane sealant came out. So I filled the core and the return hose up w/water and put some compresed air to it(be sure to use low pressure). That did the trick. Tons of stuff flowed out. Heater works great now. Good luck. <img src="/forums/images/graemlins/cheers.gif" alt="" />