[jrnsr]

I don't mean to rain on your parade, but...

First off, automatic transmissions use engine coolant for cooling, not to heat up. The torque converter can generate a lot of heat. I had an old DeSoto and it was ventilate for cooling.

If you try to "braze" the casting, you risk the chance is screwing up tolerances. It is a real pain to sweat and the attachment can be iffy, especially if you want it watertight. If you succeed on the bench, you might find after numerous thermal cycle, a leak could become a catastrophic overheating episode on the road.

When I "braze" aluminum, I use a fattened piece of stainless welding wire and scrape the molten "solder" and basemetals to coax bonding. Unless you grind the casting down to new metal, the contaminants are going to be a real issue.

50 psi air pressure would likely destroy your work. 15psi is all it'll encounter.

In the good old days, 90 weight oil went into the rear end and transmission. A Honda was the first car I had that used 10W30 in the manual trans, so they already have built the transmissions around thinner oil. Not sure what the newest cars are using. Heating it thinner may jeopardize the trans.

About a month ago, I discovered a previous owner used gear lube in the trans. iI changed it back to motor oil.

If you want thinner oil, toss in a cup of diesel and then cross your fingers.