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Discussion Starter #1
I need to replace my core because one of the copper lines that sticks out of the firewall in the engine bay cracked. Which of the two lines is the one that is actually part of the core, the left or the right one?
 

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the line closest to the steering column is connected via a rubber coupler. either way, accessing, removing, and replacing that line is a nightmare without taking the entire dash out.

my actual heater core developed a crack earlier this year. I replace it by taking the dash out. Honestly, its not that bad... just time consuming.
 

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From Beerburner at Miata.net:

There are two ways to do it. The first involves removing the dash. I don't know that way...

The second way is what I've done. Hopefully I'll remember all of the steps, although I'm sure someone will fill in any blanks that I leave.
I can also add pictures later (too dark and too cold outside) if you need them.

1) First, drain the coolant. You really only have to drain enough to get it below the level of the heater hoses so that when you remove the heater core you don't have the whole thing dump inside the car. This isn't too hard if you use the drain plug on the radiator but if you pull a lower hose, well, just empty the whole thing.

2) Remove the two screws that hold the panel under the steering wheel. The panel should then come out.

3) Crawl into the footwell and look for where the heater hoses go into the heater box. There is a whitish cover on the vertical side of the heater box that hides everything. Unscrew the two screws on that cover and remove the cover.

4) There are three little tabs that clamp around the metal heater pipes. Loosen the screws so that you can rotate the tabs off of the pipes. You can remove them completely but I find them to be a bit of a PITA to put back in.

5) There is a long pipe that runs up to the firewall and a short pipe that has a rubber hose on it. Loosen the clamp for the rubber hose on the short pipe.

The long pipe is the reason that they say you should take the dashboard out because the pipe will not clear the various things under there. If you cut the pipe as close as you can to the heater core, you will have the clearance to slide the heater core out. I used a Dremel tool with a cutting disk to do this due to the lack of space. Just make sure that you cover the footwell with a towel or something to catch any spilled coolant that may drain out. Eye protection probably isn't a bad idea if you're using a Dremel tool.

6) After cutting the long pipe, pull the heater core out and angle it down to remove it from the heater box. Be prepared for the coolant to spill out. You'll have to remove the remainder of the long pipe by going into the engine compartment and disconnecting it from the heater hose.

7) On the new heater core, I cut the long pipe about halfway between the first and second bend. (Sorry about the blurry picture.) Install the loose part of the pipe that you removed back through the firewall and reattach the heater hose. It would help to have a second set of hands for this part although you could probably do it by yourself if you want until you have everything put back together.

8) Cut a 2-3" length of 5/8" ID (I think, you should probably measure it in case I'm wrong) heater hose and slip it over the long pipe. It probably wouldn't hurt to use another similar length of hose to replace the rubber hose that attaches to the short pipe.

9) Slide the new heater core back into the heater box and slip the two rubber hoses back on and use hose clamps to hold them all in place. (Of course, you'll need to buy some hose clamps for the hose you're using to reattach the long pipe.)

10) Tighten and reinstall the three little clamps.

11) Fill the coolant back up, run the car and check for leaks. If it's all good, put the whitish cover back on and then the lower dash panel under the steering wheel.

All in all, the first time I did this it took me two hours to do. I had to do it again a few days ago (only took one hour this time!) because my crappy aftermarket heater core leaked again so this is all fresh in my mind. Like I said, I can get pictures if you want and I can edit them into this post. You'll just have to wait until tomorrow.

Or remove the dash.

I'm sure there is something elsewhere on the forum or on the garage section (click the garage link below, if someone didn't already answer all of your questions while I was typing this up!).

Hope this helps!

BB.
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Discussion Starter #6
I am asking because I don't have a replacement of the line with the rubber hose attachment and the left copper hose is the one that has the leak, so before I tore everything apart I wanted to make sure I would be okay.
 
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