thanks everybody for the help on this.. I was also not getting heat so I followed all advice here.. I took my time.. let CLR sit for a good while.. flushed good and put it together.. I got improved heat but only lasted a short while and no heat again.. I notice the coolant tank was low so I filled it and got some heat again but it lost fliud again.. never did see an actual leak but there was signs of moisture around bottom of coolant tank so following advice of another series on these forums ..I pulled the tank and ..yep.. a crack.. so I replaced the tank.. NOW THE KICKER.. backing up to AFTER the flush I had heat except with fan on High it would start blowing cool air after a couple minutes.. the more you turned the fan down the warmer the air... So now back forward to new coolant tank.. no leaks.. coolant tank lever as indicator says.. but same problem with air.. It is like the heater core is not getting full circulation and the high speed dissipates the heat.. anybody ran into this..