cruiser
Well-Known Member
Good evening boys and girls! I hope that our bedtime stories have helped you to sleep soundly over the past few months. Tonight's story covers the heater resto in my 1974 Plymouth Gold Duster. I'm sure that your heater is near and dear to you if you live up north, as I do. We've all likely been in a car with a malfunctioning heater at some point. Miserable, wasn't it? Like most of these old Dusters, the heater wasn't working properly when I bought my car in April of 2019. So one of my first priorities was getting the heat back in my new ride, and it was surprisingly easy to do so. Like everything in the 1974 Duster, the heater system is very simple and straightforward. It consists of the heater box under the dash, two heater hoses that tap coolant off the engine to keep you warm, and a simple cable operated control panel in the dash. Step one was to order up a new heater rebuild kit from Detroit Muscle Technologies. They supplied a very complete, high quality kit that was simple to understand and install. Once this arrived, I referred to my factory shop manual to remove the heater box from under the dash. This procedure begins with disconnecting the heater hoses, then removing the two control cables and the wiring harness to the fan. Next, I removed the three firewall mounting nuts and the hidden support rod inside the right side vent plenum. The box assembly was then removed from under the dash and went to the bench for disassembly. The first photo is of the heater box from another Duster that I restored. This box actually had the correct heater core in it, unlike my current Duster. I went on to disassemble this box, revealing the debris laden heater core (second photo). There is really nothing to prevent leaves and other stuff from accumulating in the heater, so it eventually clogs up the front side of the core. Anyhow, back to my current Duster. The core itself came out next. Once everything was apart I cleaned it all in soapy water, removing decades of dirt and grime. I concluded that the existing heater core was not the factory original, as the heater inlet tube was the wrong diameter. On the 1974 Duster, the heater inlet hose is 1/2" ID, and the outlet hose is 5/8". Since both were 5/8", I could tell that at some point the heater core was replaced with the wrong core. I was able to find a correct new core online. These heater cores are beautifully old school - copper side tanks and core, galvanized steel frames, and brass and copper outlet tubes. All of the metal parts were soaked in Evapo-Rust to eliminate any corrosion, then treated with Rust Prevention Magic to prevent any further rusting. The original date coded fan motor was cleaned up and reinstalled onto the motor plate, which then went back onto the rear of the box. Now that everything was clean, the new core and gasket kit went in then the box was reassembled (see photos of rebuilt unit). There are quite a few gaskets in the heater box, by the way. All were worn, deteriorated and coming apart. The cardboard (yes, cardboard) heat outlet vent was in awful shape, but the rebuild kit included this as well. The new stuff is just lovely, far better than the the quality of the original material. However, I had one more problem to tackle before the heater assembly went back in. My car came with the wrong sized heater inlet fitting in the cylinder head of my slant six motor. It should have been 1/2" ID, but it was 5/8". These fittings are nearly impossible to remove, so I had a local mechanic heat the fitting up with an oxyacetylene torch which enabled him to remove it. Without the torch, that fitting would never have come out. So in went the new 1/2" heater hose inlet fitting into the cylinder head and all was well. I installed the rebuilt heater box under the dash, being sure to install the hidden support rod in the right vent plenum. I then installed and adjusted the mode control and heat control cables and reconnected the wiring harness, and cleaned and lubricated the control panel. I then installed two new heater hoses - 1/2" for the heater inlet (with a new 1/2" backflushing tee), and 5/8" for the heater outlet. So the entire system was now returned to factory stock and correct. Finally I backflushed the entire system and installed 6 1/2 quarts of Prestone II antifreeze, mixed with water to create the recommended 50% coolant mixture. And so with the earlier restoration of the stock radiator and overflow tank, and the installation of a new 195 degree thermostat and NOS correct radiator cap, the entire cooling system has been returned to like new condition. And yes, it cools beautifully! With the high efficiency two row radiator and new heater core, the coolant temperature never goes above 195 degrees even on the hottest days. The heater itself works smoothly and efficiently, and the two speed fan gives me all the hot air that I need. I stay toasty warm even on the coldest days here in Minnesota! And so we conclude tonight's installment with the hope that you've become nice and sleepy. Get into your jammies, climb into bed, and dream of a toasty warm heater. Night night!
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