Making a home-built heater core.

For The Red Subaru

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Postscript: Now Iíve used it over the first half of the winter I can say the unit does not get the car toasty warm but it does slowly de-mist the screen once the engine is up to temperature; itís not nearly as effective as the proper unit but it is adequate. So, if you canít afford a new core or your unit is not available, the home-made solution is a better option than being unable to use the car in winter.I now know I should have spent more time making a core with more, thinner, tubes.



Above: on a Devon green lane near Castle Drogo


My old 1991 Subaru L Series is pretty rare in the UK and so there are no specialist firms making cheap pattern parts. The heater core (or matrix as it is sometimes called) was leaking badly and I bypassed it over the summer with the intention of changing it for a new one before the winter set in. But, sadly, Subaru no longer list the part and no UK suppliers had one. My other L Series car does have a good one but Iím hoping to get that back on the road too and, as itís a hell of a task to remove it (all the dashboard has to come out, along with all sorts of trim, steering wheel, centre consol etc. etc..) I really wanted to do the job only once. New cores are still available in the US and Australia at about $300 plus shipping but thatís way too much.


Encouraged by a net article in which someone built a core for a Morris Minor, I bought some copper pipe and made a unit for the cost of the pipe, some solder, flux, scrap timber batten and a few hours work. It wonít transfer as much heat as the proper part but I only need enough warm air to keep my windscreen from misting and freezing in the winter Ė if I get cold thereís always thermals and sweaters.


With the whole dashboard removed (several hours if you take it slowly), the heater box is to be found up against the bulkhead. How good it was on old cars to be able to get to the heater without removing everything.




Above: the dashboard has been removed from the car. Hereís the heater unit with its bellows operated ducts.


Once the heater unit was taken out of the car, the core is accessible:



Above: the top of the heater core with evidence of failed water additive to stop the massive leaks.


I then removed the heater core and took it to the kitchen sink; the water was pouring out of the bottom as fast as I could put it in. As itís a composite unit of old brittle plastic and metal pressings, repair was out of the question.


To ensure my copper pipe construction would fit, I made a wooden jig from scrap timber batten and screwed my copper inlets and outlets in position to the same measurements as the old core. The rest of the pipe-work was bent in several sections with a manual pipe-bending tool and joined with standard joints. I knew that as long as the pipes fitted within the jig, they would fit within the heater case.


Here is the rough assembly sitting in the wooden jig; the dimensions are not spot on at this stage and some pipes were adjusted slightly for length and curve. The inlets and outlets were the only bits to be soldered in advance and they were at one point screwed with pipe clips to the top of the jig.



Above: The old unit on the left compared to the one being built on the right.

Next, the assembly was finalised as a free-standing unit.



Above: the unit nearing completion.


Once out of its jig, the unit required further adjustment before being soldered to ensure the inlet and outlet were an exact fit with the pipes feeding the heater box.



Above: soldered up and attached to the feeder pipes.


The plumbing joints used were the Ďpre-tinnedí types that have a bead of solder already inside them. I fluxed the tube ends and, using a cheap blow torch, added solder to the outside of each joint in order that the joints cope with the added pressures of the carís cooling system. At this stage, the whole has been soldered and the feeder pipes have been attached. I then blocked one end and blew hard into the other while holding the assembly submerged in a bucket of water; no bubbles, no leaks.



Above: the completed unit being lowered into the heater box. The pipe bending tool is on the right.


Iím pretty pleased with the result. The unit fits very well. My only concern is that this crude (though nice looking) replacement part will not provide enough heat. On a test run (after the several hours it took to replace the dashboard and all that went with it) I could not get the engine up to temperature even though it was a hot day (29˚C) Ė previously I had been running without a thermostat all summer due to overheating!So clearly, heat is being lost through the new unit. Letís hope itís enough to demist a frozen windscreen come winter.



Above: the heater box with the new unit fully fitted.


My next task is to put the thermostat back and see ifI can feel much more than slight warmth above ambient.


If youíre thinking of replacing the heater core in your car and youíre scared of removing the dashboard, there are some useful tips that make the whole experience a bit less daunting. Divide the task into manageable chunks and take lots of pictures as you progress so that you have a record of what goes where. Use several containers for your screws, nuts and bolts, clips and small parts and label each container. Put the containers on a shelf in task order and youíll have a ready-made aide-memoir for re-assembly. Take photos of wiring that you think might be complicated to put back: I was luck inasmuch as Subaru have used a huge variety ofshapes and colours of connector so few are easy to mistake for one another. Donít rush; give yourself a long weekend for the job; a day to dismantle, a day to check how it all fits (and/or to make a core) and a day to put it all back Ė enlist a helper if possible to replace tricky items that otherwise would need an octopus . Take plenty of tea/coffee/cigarette (damn, Iíve given up) breaks and stick to the instructions in your workshop manual.



Above: The Subaru in its element


Nick Nakorn 2012