Strong coolant smell when the front heat is on. One time see coolant on the floor from the passenger side after filling up the reservior to the line. But no more leaking is seen when the reservior is only 1/4 full. Also noisy sound comes out from blend door when switching from cool to hot. Could be heater core leaking? If so, is it hard to replace? Thanks!

What engine is in the vehicle, how many miles are on it, are you getting any codes thrown?

The heater core is not that difficult to remove .... if done correctly. But make sure it's the problem. Do you see water coming out the drain spout, or inside the cabin?

1. Drain coolant system ... doesn't have to be totally empty, just very low.
2. Remove plastic cowling. Reach down behind engine and disconnect hoses from heater core at firewall. (At this point you could test the core to see if it will hold 20 psi of air pressure.) Plug inlet and outlet tubes with rolled-up plugs of paper towels. (To prevent spillage inside cabin as you remove the heater core ... inside the cabin).
3. Gain access to heater core and heater core (belly) cover inside the cabin. What all this intails ... depends on which trim level and year model you have. If you are a contorsonist .. it won't require as much removal of "stuff" ... but, if you are a big 'un like me .... well.
4. Remove the core and plastic belly cover together! The core lies flat inside the cover ... all under the interior ac/heater plenum, inside the cabin, under the front console. The heater lies somewhat under and in front of the radio area. If you try to remove the cover and then the core ... you will have major buised knuckles. The cover is held in place by (seven, I believe) screws. There is one screw, in the center, behind the cover against the firewall ... after you get this one, the rest are easy.

What engine is in the vehicle, how many miles are on it, are you getting any codes thrown?

It is 3.8L. The trim is SE. It has 90K on it. Everything else seems working ok (knock on wood) for now.

The heater core is not that difficult to remove .... if done correctly. But make sure it's the problem. Do you see water coming out the drain spout, or inside the cabin?

1. Drain coolant system ... doesn't have to be totally empty, just very low.
2. Remove plastic cowling. Reach down behind engine and disconnect hoses from heater core at firewall. (At this point you could test the core to see if it will hold 20 psi of air pressure.) Plug inlet and outlet tubes with rolled-up plugs of paper towels. (To prevent spillage inside cabin).
3. Gain access to heater core and heater core (belly) cover. What all this intails ... depends on which trim level and year model you have. If you are a contorsonist .. it won't require as much removal of "stuff" ... but, if you are a big 'un like me .... well.
4. Remove the core and plastic belly cover together! The core lies flat inside the cover ... all under the plenum. If you try to remove the cover and then the core ... you will have major buised knuckles. The cover is held in place by (seven, I believe) screws. There is one screw, in the center, behind the cover against the firewall ... after you get this one, the rest are easy.

12OUNCE - thanks for the info. Read some posting you had on blend door/actuator. Thought heater core can be accessed from inside. Do I need special tool for this task?

Well, I see my words were confusing ... I'll go back and edit.

No special tools required unless the radio is removed for more working room. Then you would need the OEM radio removal tools available "everywhere".