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© 2001 Brian F. Schreurs
Even we have a disclaimer.

So it was disappointing, but not really surprising, when a passenger reported hot engine coolant pouring on his foot. The dread heater core had finally let go. This is a device that most hot rodders have heard of, but far fewer have ever actually seen. It's one of those parts that enthusiasts apologize for taking to a mechanic, saying they would have done it themselves but for a "lack of time" or some such. We are not wusses. When the Paradise Garage 1970 Dodge Charger called for us, we answered the call. We replaced the heater core ourselves, thankyouverymuch.

Surprisingly, it wasn't that hard to score a replacement through a local auto parts chain. What we ended up with was Rockhill #94500. We also bought about eight feet of 5/8-inch heater hose, for reasons we shall discuss later.

One of the funny little clips that hold the door-actuator-cables in place. This one, thankfully, is the only one with a screw in it.

To start off, drain a little coolant out of the radiator so that the water level is below the level of the radiator hoses. We drained out quite a bit more than that, figuring it needed to be changed anyway.

Undo the heater lines where they meet the firewall in the engine bay. They are normal hose clamps. Be prepared to replace them, as they might be stuck on real well and need to be cut off. If they are stuck on, slice the hose along the length of the fitting. This will allow you to split the hose and remove it. If the hose is otherwise in decent condition, and your heater core doesn't have the problem we note in a bit, then there should be enough slack in the hose to just hack off the sliced end and reconnect it later.

The inside of the glovebox has to come out to provide access to the heater box. It is just cardboard so be careful; it's held on by several Phillips screws. It can be rotated backwards and slipped through the glovebox opening. The door itself is prevented from easily falling off by its hinge; the hinge has a rubber stopper on the inside that is reistant to sliding through the slot. It will fit though; just takes some persuasion. Alternatively, it's a bit easier to simply remove the two Phillips screws retaining the hinge to the door and taking the hinge out the back. The screws holding the glovebox latch do not contribute to holding the glovebox liner, so leave them in place.

Lots to see here. Extreme left, note two wiring looms: one exposed, one braided. Both must be moved. Also note wiring bracket on the far end of the heater box. Middle, the two defroster vent ducts. The actual tubing is somewhat flexible and tucked above. Extreme right, note the two plugs for the blower motor. Black cable running through the middle is a detached defroster door actuator cable, constantly in the way.

Unplug two plugs going to the blower motor. Just above the plugs, there is a bulkhead brace held on by a 7/16" nut. Remove it.

Think you can just remove the faceplate to swap the core? Think again. If you take the faceplate off, you'll be able to look at the heater core, but you won't be able to get at it. The entire heater box, yes, that huge black thing that extends from the passenger door to the gas pedal, has to come out.

Disconnect the flap control cables by pulling the cables off the levers (one is on the front of the box, passenger side; another is on top of the box, directly behind the glove box). The front cable retaining clip has a Phillips screw on our car, though we suspect that was added later; the top one just pries off. There is a third one on the driver side, just above the two defroster vent tubes (which also need to be pulled off the heater box). Also watch out for the wire harness support bracket on the extreme driver-side of the heater box.

The two studs on the passenger-side, left, and the one stud on the driver-side.

The heater box has three studs that hold it to the firewall; the nuts for these studs are on the engine-side of the wall. Two of them are plain to see below the heater core outlets. The third is tricky, hiding on the driver-side, directly behind the engine' valve cover, hidden by a wiring harness. But it's there. All three nuts are 1/2".

With everything unplugged and unbolted, the heater box can be wiggled free. The antenna wire may get in the way when you try to move the box (so unplug it!), but other than that, it's simply a matter of patience while gradually working it from under the dashboard. Generally twisting it axially toward the front of the car seems to help.

When you have the heater box out... oh. Okay. We'll wait.

The heater core in its natural habitat.

When you have the heater box out, remove the back plate to get at the heater core. It is held on by 13 sheetmetal screws that take a flathead screwdriver. Also unplug the elbow hose from the blower motor, and remove the two socks that fit over the heater core outlets. Then, the core is held in place by four more sheetmetal screws: two along the bottom and two along the top. The top ones are longer than the rest.

Installing the new core is basically the same as removing it. Screw everything back together on the box. Then try to get the box back into the car.

Ha ha! Isn't that fun? Hard to believe it actually came out from there, eh?

To get it in place under the dash, the box must be tilted forward, so that the electrical plugs are facing up. It wiggles in eventually. No, really. Keep trying.

The clips for the door cables are kind of annoying but just snap in place -- eventually. The cable that attaches on the driver-side of the heater box, by the way, actually makes a loop going from the driver-side, over to the passenger-side, and back to the driver-side.

Old and new. Hopefully we won't get to see this for another 30 years.

You'll need an assistant to guide the final alignment of the box. He should watch from the outside of the firewall for when the heater core outlets and the bolts show through. Then have him get those nuts back on there while you hold it in position.

Don't forget to reattach the defroster vent tubes.

Reattach the glovebox door and insert the cardboard glovebox liner, or what's left of it.

Make sure the heater hoses have a clean end to them and reattach, unless you get a heater core like ours. The heater core we used didn't match the original. The original used two different sizes of hose: 1/2" and 5/8", whereas the new one used two 5/8" hoses. Wankers! How hard is it to install original fittings?? We had to buy new hose, since there's no way to get a 1/2" hose onto a 5/8" fitting. But our hose was kinda skanky anyway, so we just figured it was par for the course. We bought new hose and new clamps (buying new hose is always a good excuse to replace the clamps too!). To route the heater hoses in their original location takes just a little less than eight feet total.

The car is so much faster now, it's unbelie... oh, wait. Wrong article. The, uh, heater works again! Yay! The heater definitely works with authority, and our passengers no longer get a hot foot soak when they go with us to the local cruise-in. And, best of all, we don't have to apologize for taking it to a mechanic. We dun it ourselfs!