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MG MGB Technical - Heater help!

I just removed my heater matrix as it appeared to be blocked, I back-flushed it and now it I can blow through it ok. However a couple of issues;

1) There is the white tell tale sign of a very small leak from one of the matrix tubes, where it's soldered to the end tank. The heater distribution flap was a bit wet, but there's never been any coolant in the car. My guess is that it evaporates away. the car doesn't noticeably use any coolant. The question is what to do about it. I'm not buying a new one. I've done quite a bit of plumbing soldering, would it be worth having a go with a plumbers torch, trying to re-wet the joint and add a bit more solder. I've successfully solder a radiator in the past. How about filling the matrix with rad-weld or a bit of super glue on the outside?

2) Second question is that there's a foam seal block around the bottom of the distribution housing, it's not shown on the Moss parts catalog and the demister pipes fit directly into the distribution box so I can't quite work out what it might have been for. Was is a sound deadener or some thing. It's well past it's prime and I'm not sure if I need to keep it, but it must have doen some thing. It's not to be confused withe seal of the heater box to the body. My car is an original V8, I don't believe this makes a difference.

Many thanks for any help. It was quite a job getting it out and I don't want to have to repeat it.

James Eastwood
James Eastwood

You really don't want to do this job twice, so getting it right the first time is mandatory. A new matrix is less than $100. I went through this ordeal 20 years ago and not one of the usual parts suppliers had a new matrix in stock. I had two spares that were as old as the one that I had removed from my car. I pressure tested them using an old inner tube and some hose clamps while pressurizing them with a tire pump. One was a little questionable. The other seemed to hold pressure over night. I installed it and it has held up for twenty plus years. I got lucky. You may be able to find a used matrix at a salvage yard, but you are risking having to do the job a second time. I would try to locate a new unit. The foam block is to retain the demister tubes in place. RAY
rjm RAY

The foam is exactly what you said "a seal". The later demister tubes clip into the back of the central bracing, and the foam fills the gap between this and the bottom of the heater box . Make your own!! You want some fairly dense foam, some people have moulded their own using a building foam can. Definitely buy a new matrix, the job's a real fiddle, not to be repeated too often.
Allan Reeling

Ray, Allan,

Thanks. I liked the inner tube and pump test idea, I've set up my own testing system, similar to what Ray described. I'm testing at 15 psi as that is the radiator cap pressure. I've got the whole matrix submerged under warm water, the only issue is it's not showing any sign of leaking (bubbling). I may repeat with water as hot as my boiler will provide.

Still not minded for a new matrix as they're £70.

I shall post progress! James.
James Eastwood

Can you not try your local radiator specialist?
Dave O'Neill2

I resoldered a split in the soldered joint twice on my V8 radiator but it opened up again, and eventually I swapped it for a new (uprated as it happened) unit.
PaulH Solihull

I agree with using existing parts wherever possible but in this instance with a standard (or uprated) matrix from eBay delivered to your door for less than £60 it doesn’t seem worth the risk to try to reuse one that you know leaks.
Geoff King

I managed to replicate the leak at 2B (30psi), running pressure is up to 1B, but I have assumed that although I tested in warm water, full hot coolant creates more stress in the unit contributing to a leak at 1B, added to which there is also teh vibration.

I cleaned up the area with a small wire brush, then re-soldered it with plenty of flux to clean the joint. After a couple of attempts I managed to get a really good continuous bead of solder down the side of the tube where it had leaked adjacent to the end tank.

Quietly confident I'd done a rather good job, I put it back on test under water..... and it leaked more and at a lower pressure.

I can now tell you that Moss have a sale on at the momment and I am happily in teh good company of every one else who did not repair their heater cores!

Thanks for your help. James
James Eastwood

This thread was discussed between 01/12/2012 and 03/12/2012

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