so i have put 2 different heater cores in my ef, the first one i knew was bad the second one i was told was good so i installed it, everything is hooked up, ( and i mean everything ) is it possible for a heater core to be bad but not leak ?? i have one hooked up right now ( supposedly good ) with the whole dash out and i hooked the lines up and made sure the valve was open and it is and it just doesn't get hot, my blower works fine it has plenty of pressure blowing in but wont get hot, i have the line from the head running into the bottom hose and the return coming out the top, still no hot air, so im guessing the heater core my cousin told me was good is a pile of ----

 

possibly, there is pressure in the feed but not the return, ill use my compressor and make sure the new one is extra good

 

spray it with the hose.. if water comes out the other end.. you know its not clogged

 

Exactly, can't get much easier than that.

If it isn't clogged, and it still doesn't get hot, suspect a blown headgasket or T-stat problem.

 

My cable on my air mixer door got stretched out at it wouldnt blow all the air through the heater core and would just feel kinda warm not hot. Im sure uv checked just thought i would through that idea out there.

 

not a h/g maybe t stat, i dont even think im running one :P

 

I think you answered ur own question. What is the temp like in you're area?