Install Heater In ’74 Duster

Tech Question


Bobby Croak, indianapolis, IN, 1974 Plymouth Gold Duster 318

I would just like to say first that I am 17 and I love your magazine. I have been reading MoparAction for a few years now and I think you guys do a really great job. My question is how do I install a heater core in my 74 cold Duster? It currenly has a 318 but my dad is going to help me install a 440 in a few months. Would it be easier to wait untill the swap or go ahead and do it now? My dad works all the time and I never have time to ask him for help.



Cold Duster, huh? I guess so, with a non-functioning heater! Hey, it’s still way better than the more common Rust Duster model, right? And I’m sure you have a girlfriend, so it can’t be that cold.

Speaking of cold, you didn’t mention A/C, so I will assume there’s none.

The core is slightly easier to swap with an empty engine bay, but not my much. Most of the work is under the dash, and that’s not affected by the engine removal. Under the hood, remove the hoses (which, presumably, you have done already!) and the nuts holding the heater box studs to the firewall, leaving 1 or 2 of ’em on finger loose. If you’re worried about coolant spillage inside the car, blow out the core, through either fitting, with compressed air – all the pressure you’d like – the core’s already trash, right? If there’s a small plate surrounding the nipples, remove it (one screw in center).

Inside the car, remove the glove box liner (from the front) – this step greatly eases access to the cables. Then remove the defroster hoses from the heater box, unplug the fan wiring, and unclip the control cables. If the cables aren’t color coded (they should be) make a clear sketch, or take a pix, of how they were routed and connected. Then remove the long J-hook that retains the right side of the box up to the cowl – you’ll find one long, small-diameter, dog-point screw on the bottom, under the fresh air door. If you can’t visualize this, just look inside the door with a flashlight and it will become crystal-clear.

While you remain insdie holding the box, have an assistant remove those loose nuts, and drop the whole box out.

Once safely on the garage floor, bench, grass, etc, simply snap (pry) off all the clips holding the 2 halves of the core box together, and remove the rear half (the side away from the firewall.) Now the core installation is pie.

If you find various seals and gaskets that are shot (miracle if you don’t), you can make good replacements from that common thin white shipping foam wrap, a razor knife, and contact cement. The thick gasket (up top, at the cowl air inlet) can be functionally duplicated with Home Depot weatherstripping.

Then just slam it all back together, taking care not to damage the nipples on the new core when sliding ’em through the firewall.


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