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Project Marina, Heater Box Repairs

Progress on the Marina has been slow. I had hoped it would be on the road by now, but that’s not happened.

The good news is that any progress, is still good progress, and some headway has been made.

I have really battled with the heater box and dreaded trying to fix it. In reality, getting it into a usable state wasn’t that hard. Negative mindsets can be a real pain like that.

According to my records, I removed the intake plenum box way back in October 2021… that’s how long it’s taken me to get around to sorting it.

The heater/blower system is completely bespoke to the Aus/Nz spec cars and differs greatly from how the UK ones are set up. This was obviously due to the local content requirements of the time, which meant a percentage of the car had to be made locally and not imported.

This car came with the heater box in the boot, so I’ve never seen it fitted to the car. The plenum box, which is mounted up under the cowl panel behind the dash, was in place but full of dirt and old leaves. Not a good sign.

I removed the grille and then set about removing the screws that hold the plenum box in place. Once removed, the whole box just drops down.

It was pretty well full. Took a lot of vacuuming to clean it out

But the main reason it needed to come out, was to fix this

The metal has ceased being solid and became a crunchy powder.

Here it sat for a couple of years, until almost 2 years to the day later, and I pulled it out to have a better look. This involved lots of cutting and drilling, to remove the spot welds and remove the rusty remnants.

The gaping hole in the side is obvious, but there were also a lot of other areas that needed attention too, in harder-to-reach places

After cutting all this out and cleaning it up as much as I could, I absolutely saturated it in Brunox to treat the rust and seal it off.

Because my car is a poverty spec Deluxe and doesn’t have the face-level fresh air vents in the dash, I opted to just completely remove the tube for that function on this side as it was completely rusted out and the idea of refitting the tube was doing my head in.

I started with some good old CAD

Converted it into metal, and tacked it in place

I didn’t fully seam weld it, I just didn’t see the point when it was not structural

I seam-sealed the area to seal it and used Newtech body filler to smooth over the welds and fill the holes in the top that I couldn’t get to with a welder. Newtech is a fibreglass-infused filler and pretty strong, so should do well enough at keeping the air and water inside the box.

Everything got a coating of black zinc on the outside, and the inside was flooded with epoxy primer and then black zinc.

I remembered to refit the heater resistor

Someone had cut the wires for the heater resistor when removing it, so I crimped on a pair of nice new terminals, so now I can unplug the resistor if I need to

With the plenum box done, it was time to test-fit it with the heater box. Before that though, let’s travel back to 2021 when I tested and refurbished the heater box

The heater box was already out of the car, so the first thing to do was see if the fan actually worked. I connected 12v and turned it on. Sure enough, it fired into life with no signs of any issues.

I then set about splitting the box by removing all the nuts and bolts around the perimeter. The whole box is moulded fibreglass.

This gave me access to the fan and heater core. I cleaned out years of detritus and pulled it apart further

The heater core looked ok with no obvious signs of leaking

The direction flap is a little less good

The flap is actually made of two layers of metal that sandwich some sort of felt material that creates the edge seal. After cleaning it wasn’t too bad, just missing a bit on one edge. Not the end of the world.

I didn’t want to just refit the heater core and cross my fingers, so I bodged up some hose and fittings so I could pressure test it.

I filled it with water and pumped it up to 15psi (just above the rad cap pressure)

I can’t remember how long I tested it for now, but I think it was a couple of hours and it didn’t drop pressure at all. It could spring a leak once it gets hot, but I hope not.

I rust treated and then black zinc painted everything inside the box

I reassembled it, with some new foam on the diverter flap (to seal it when it’s closed), and it’s been gathering dust since.

Well, today I pulled it all out and put it together. This is the Aus/NZ spec heater assembly

The air enters the top of the plenum via the vent in the cowl ahead of the windscreen. It then enters the plenum box and gets sent to the heater box via the C shape duct on the side (the other hole is the face-level vent outlet for the higher spec cars. This is blocked off on my car.

The air then passes through the heater core (all air does, the heater valve controls if the core is hot or not), through the fan and down to the ducts at the bottom of the box. The circular outlet would be ducted to the windscreen vents while the large cutouts are the “feet” vents. The heater selector only has three settings, Feet/Windscreen, Windscreen or Off.

There should be a heater valve attached to the box too, but mine was missing and the only spare I have I don’t trust. They’re very expensive heater valves shared with some classic Aussie Fords (hence the cost), so I will likely just have a manual heater tap in the engine bay to turn the heater on and off. For now, I just have the heater bypassed.

The test assembly was a success, so I contorted myself into the car and started refitting it. The plenum went in easy enough, once I turned it around so it faced the correct direction. I used a ratchet strap to hook into the plenum box just to give me something to lift it up from the floor inside the car while standing outside, as the screws to secure it go through from the outside.

The vent grille could then be refitted, with some nice new screws

Next, it was a case of fitting the heater box to the underside of the plenum. This turned out to be a bigger pain in the bum than expected. I fitted it all up, nice and easy, no issues, and then realised I couldn’t fit the C-shaped duct in afterwards. So out the heater box came. I fitted the duct to the plenum first and then squeezed the heater box into place.

This took an awful lot of wiggling and jiggling to get into place, from both sides of the car. That was the easy bit though, the hard bit was getting the cable for the diverter flap into place. This is in the drivers foot well, so I squeezed myself into there and hooked it up.

Next, I connected the blower fan wires, connected the battery and hit the switch. Nothing. Hmmm. I tried again, flicking the switch a few times and suddenly it sprung to life. I guess sitting around unused for a couple of decades does that to a switch.

But both speeds work correctly now, so I’m very happy

I still need to buy some ducting to duct it up to the windscreen vents, but for now, it’ll do.

Following that success, I felt it was time to fit something else the car hadn’t seen for many years. For the first time in my ownership, the car has steering column shrouds

I did have to relocate the ignition switch though. Turns out it’s not meant to point down; the previous owner just didn’t clock it to the column properly (and disabled the steering lock in the process) when the switch was replaced. It fits perfectly now, and the steering lock even works too. Makes way more sense having the key where it is, it was always hard to see and use when it was facing down.

We’re getting much closer to being able to take it for a WOF check. I need to refit the quarter window, which I’m procrastinating because I haven’t done it before and I’m sure it’ll suck to do, and then fit some door cards, seatbelts and the other seat.

In the meantime, I scuffed up the new sill and gave it a quick shot of paint

Theres a low spot on the rear quarter that I want to address before I put any more paint on that. Might do that this weekend.

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