How Do I Change a 300M Chrysler Heater Core?by Renee Booker
Replacing the heater core in a Chrysler 300M is a very simple process well within the capability limits of the average do-it-yourself mechanic. The entire process should take less than two hours and requires no special tools or manuals.
Drain the cooling system. Draining the cooling system will prevent toxic engine coolant from leaking into the passenger cabin of the vehicle during removal of the heater core. To drain the cooling system, simply disconnect the lower radiator hose from the radiator by loosening the hose clamp and pulling the hose off. Be sure to drain the fluid into a sealable container and dispose of the coolant at an appropriate disposal site.
Pull the dashboard six inches rearward. In order to do this, you must remove the following parts; the center dash bolt (located under the defroster vent cover), the bolts under the driver and passenger kick boards, the bolt connecting the dashboard to the radio mount, and the the bolt connecting the dashboard to the rear of the glove box. The locations of these bolts are immediately apparent upon looking under the dash. Once you have removed these bolts, you can pull the dashboard rearward and secure it.
Remove the heater core box. The heater core box is a black plastic box that surrounds the heater core. This part should be visible when looking down into the dashboard from the passenger side seat. Remove the two bolts on top holding it to the firewall and another on the bottom near the foot well. After removal of these bolts, the heater core and box are attached to the vehicle only by the coolant lines, which you can now disconnect by reaching into the box and pulling them off of the heater core (you may have to loosen the clamps first).
Install the new heater core. This is accomplished by applying steps 1 through 3 in reverse order; re-connect heater core coolant line, re-install heater core box (be sure to apply silicon sealant to the edges of the box, hermetically sealing it), replace the dashboard and install bolts, and re-fill the cooling system.