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March 27, 2014

Coolant Return Tube

The TR6 engine has an external 1/2 inch steel tube that returns coolant from the heater core and the intake manifold heater at the rear of the engine to the water pump housing at the front.  It runs under the exhaust manifold, so it's exposed to pretty harsh conditions, both inside and out.

The tube on my car was pretty severely rusted on the outside, and totally clogged on the inside.  After derusting, there wasn't much left in some places.  The passage in that little stub pipe is open only because I drilled it out.

I considered the tube toast.  There are aftermarket replacement tubes available, even stainless ones, but considering the probability of disappointment with the quality of aftermarket parts, the return tube seemed like a good candidate for a home-made replacement.  I determined that whatever the replacement turned out to be, it should be made of some more durable material, like stainless steel.

My first attempt at making a replacement consisted of a stainless tube (left over from the replacement of the intake manifold heater pipe) and stainless plumbing fittings.  When it was finished, I thought it looked kludgy and clumsy, and it didn't reproduce the positions of the tube connecting points very well.

One of the reasons I wimped out and used a plumbing elbow is because I didn't have a good way to bend stainless tubing to the necessary radius.  I took a day or two to modify a bender I had, and started on a new, more encouraging path.

I now had a pretty good bend, but I still didn't have high confidence in my ability to make a good looking weld for the stub pipe.  Instead, I found a piece of 3/4" hex stainless to make a "T" junction.

I cut off the hose barbs from the fittings from the previous attempt and adapted them to fit into the drilled hex.

Then silver soldered the T block together.

I cut the other end of the tube to length for a new stainless compression fitting.

I like this approach much better.

Now to make the little support bracket for the rear of the tube.  Another reason for the hex T junction was to give a place to attach the bracket to the tube assembly.  I wasn't sure I could do a good weld directly to the tube.  I got a piece of 1/16" stainless sheet and after making a cardboard template, cut out the bracket, bent it, and drilled it.

I attached the bracket with an old surplus spot welder I have, but silver soldering it might have been cleaner.

The tube came out pretty well, and looks nice.  Too bad it's mostly hidden.

I had a little of the stainless hex left over, so I made a barb fitting to replace the one at the top of the water pump housing.  I'd already zinc plated the old one, but it still looked pretty sad.

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