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MG TD TF 1500 - Tapping into the thermostat elbow

Part of my heater project will include tapping into the thermostat elbow (51TD). Is this cast iron or steel? If steel, it should be relatively easy to drill and weld, but I'm assuming it's probably cast iron.

If so, what's the best way to approach this? I want to put an inlet for a 5/8 hose on the right side of it (viewed in place from the driver's seat) for my heater takeoff.

Gordon Lawson tapped into it but I don't know if he had it welded or brazed.

Jim Merz also took his heater connection from the thermostat elbow, and brazed it.

Ive done welding but never brazed anything.

How easy is it to braze to cast iron? I've never done it and the hottest thing I've got is a MAPP torch. I've got a stick welder, tho... wondering if there is anyway to braze with that?

Welding cast iron requires getting the whole piece up to very high temperatures, something I probably can't do, but I do know people who can...
Geoffrey M Baker

Cast Iron (CI) does not weld easily. You must preheat to at least 400F, 600F is better, you should use nickle rod. (There are special CI rods, they are usually nickle based). You must slow cool. Stick the part into a bucket of expanded mica (Vermiculite). It helps to bang on the weld joint with a ball peen hammer periodically as it cools to relieve the stress.

I usually braze using an OA torch. Generally I silver braze but If I have some Phosphorous-brass filler that works well.
I also prefer the black, activated flux.

I have brazed quite a bit of CI with success but I have had limited success with welding, although I must admit I am much much better with OA than a welder.

My daughter is a certified welder and a Journeyman Fitter.I had her try the last time and she also failed.


Jim B.
JA Benjamin

Hi Geoff. I had to have my housing milled off with just a skim cut to clean up and true up the faces. It was cast iron. It already has a 3/8 pipe threaded hole someone put in it on the Genny side of the engine. Right know I have that plugged. I plan to open that up and use it for my temp gauge. Maybe a heater in the future. You might want to just drill hole and put pipe threads in verse welding. You may already know that cast iron can be welded or brazed but needs special heating and slow cooling to keep it from cracking. Hope this helps.

RER Rosa

See http://www.ttalk.info/LawsonHeater.htm for Gordon Lawson's ideas. After tapping threads into the hole, and screwing in the short nipple, I brazed the nipple into the elbow. MAPP gas works fine with Phosphorous-brass fluxed rods. Home Depot sells a kit that has all that you need. I think Gordon brazed his, rather than welded it. IMHO, 5/8 is too big. Bud
Bud Krueger

1/2 NPT tap. Bud

Bud Krueger

The fitting: Bud

Bud Krueger

Tapped

Bud Krueger

Installed (before trimming)

Bud Krueger

Trimmed

Bud Krueger

Brazed (then cleaned up and painted) Bud

Bud Krueger

Geoffrey,
Four years ago I drilled and tapped the elbow. I put some water sealant on the nipple threads, screwed it in and cleaned up the insides. Then I screwed on a coupling for my thermostat. The use doesn't matter.
It's a none pressure system and although it goes through temperature changes I've never had a hint of a leak. No welding. No brazing.
Just my two cents.
Mort

Mort 50 TD

ok, between this and Geoff's previous thread and that wonderful link in it I'm totally confused so please help me with two simple questions: Does the water flow into the pump through the side hose and out through the back of the pump into the block? Does the water flow down in the radiator? Thanks. Jud
J K Chapin

Jud, the water flows INTO the pump and into the block. Then it rises (by thermosiphoning and by the small pressure caused by the pump impeller) through the block and out into the radiator via the thermostat. The thermostat contains a bypass so that when the engine is cold the water does not circulate out to the radiator but into the bypass and down back to the pump.
I didn't know this two days ago :)
Geoffrey M Baker

Thanks everybody for the wonderful input and the free educational system known as the MG BBS!
To recap, I am going to tap into my thermostat elbow, run a 1/2 inch pipe out to the heater and then feed the heater back into the lower radiator hose. I'll cap and remove the current pipe connecting to the back of the head. I plan on running my heater pipe below and behind the manifold to reduce clutter. And lastly, I'm going to install an electric 12v valve (probably in the engine bay, not behind the heater in the passenger compartment) which will let me shut the water off to the heater when I don't want it.
Because I'm going to connect in BELOW the thermostat, I don't have to worry about bypasses. I'll restore the original bypass that connected the thermostat side connection to the lower radiator hose.
I believe from the research I've done that this will give me the most heat when I want it, no heat when I don't want it, and the least interference to the original thermosiphoning system.
It will probably be a while before I have assembled all the parts and done the work and am ready to install this... and of course, when I get started who knows what issues I will find when cleaning and rebuilding the heater itself...

But in the meantime, I'm back to working on my convertible top... I just stapled up the header bar, and am working on getting the placement of the top just right.
Geoffrey M Baker

Jud, see http://www.ttalk.info/XPAG_Cooling_System.htm for Gene Gillam's detailed show of the path of the coolant through the engine. Bud
Bud Krueger

This thread was discussed between 25/10/2014 and 26/10/2014

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