67 Caddy Gets A New Heater Core

We decided to tackle the leaking heater core in the 67 Caddy today.  There had been a slow leak and occasional fogging of the windshield, so we knew we had to get in there and get it replaced.  We located the part online for a good price (thanks Rock Auto.com!), and set about installing it.  The install was pretty straightforward without any real surprises.    Some of us showed up on time, some a few minutes late, and others completely missed the show.

Start by disconnecting the heater core lines.  We didn’t feel like letting the car cool down, lol.  So we had a little steam. 

Disconnect the electrical wires and a few of the vacuum lines that might be in the way.  Then remove the electrical/vacuum modules that are held to the heater core housing. 

Disconnect the long black bar on the passenger side so you can get the heater core housing out the passenger side.  The housing itself is held to the firewall via 5 screws and 1 nut (3 screws on bottom, 2 screws and 1 nut on top).  Then lightly pry on the housing to seperate the sticky gasket from the firewall.   We also removed the vacuum module on top of the heater core housing.  The vacuum lines pull off as one piece, then remove the module.  There is a gasket between the housing and module, ours was pretty well shot, so we repaired it best we could an sealed it up with a light coat of RTV.  It does need to be air tight for the vacuum system to work properly. 

Once everything is loose and out of the way, you can pull the housing out.

On the backside, remove the 6 or so screws holding the heater core / vent plate to the housing cover.  Once you remove that, you can then undo the heater core retaining straps, remove the old core, replace with the new, and reinstall!

After our test run, it appears the climate control unit is working in terms of directing heat to the defroster, floor, etc, but we think there is still a temp switch issue as the fans never kick down once the interior warms up.  Stay tuned on that.