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April 13, 2016


Engine cooling on the TR6 is provided by a traditional pump-assisted thermosiphon system.  When the engine is at operating temperature, waste heat is loaded into the coolant, which circulates to the misnamed radiator, where it transfers its heat to the environment.  The radiator is misnamed because its primary mechanism for heat transfer is convection, not radiation.

My radiator was pretty grody looking, but it wasn't leaking.  While cleaning it up, I was surprised at what good shape it appeared to be in for a 40+ year old original.  However, while brushing the crud from between the fins, some of the fins crumbled on a couple of areas near the bottom.  This "fin rot" is likely caused by long term corrosion from road salt.  It was limited in area, and didn't appear to affect any of the tubes.  On the other hand, it bothered me a lot. Beside the cosmetic aspect, I wasn't comfortable relying on a crucial component with unknown internal condition.

So I had a decision to make:  Replace or repair?  If I decided to replace, would it be aluminum or traditional copper/brass?  There is a holy war raging in some quarters over the  question of copper versus aluminum radiators.  Radiators in new cars are moving to aluminum cores, but this is probably influenced mostly by weight and cost.  Aluminum is cheaper and lighter than copper, but copper has better heat transfer characteristics.  In a classic car, copper looks correct, aluminum looks bling.  There is a lot of anecdotal evidence of aluminum radiators having short lifetimes, and they are more difficult to repair.

Based mainly on the spirit of this rebuild, I decided to stick with copper.  Further, due to my bias against aftermarket parts in general, I decided to have my radiator re-cored rather than buy a new one.  I went to a local radiator shop that specializes in classics for some advice.  Cliff recommended a custom made core to reproduce the original.  It wasn't cheap--it was considerably more than an aftermarket unit, but I told him to go ahead.

I asked Cliff not to paint the outside of the radiator, since I wanted to do that myself.  He did paint the interior surfaces of the frame that would be inaccessible after assembly.  

Without paint, the rebuilt radiator wasn't pretty, but I was able to see past that.  Cliff removed some dents in the top and bottom brass tanks, bead blasted all the paint and rust form the side frames, and gave them a phosphate bath.

And of course, I got to keep this.

Now since I removed the stock cooling fan, I now had to arrange for an electric fan.  I was pretty sure that clearance could be an issue, so I mounted the radiator on the car to get some measurements.

I determined that I had to keep the mounted fan depth under three inches to avoid some bad heartache.

As a side task, when mounting the radiator, I found that one of the side braces had gone AWOL, and the one I had was deeply rusted and pitted.  I decided to just make a couple of new ones.  Not sure what the center hole was for.  If I find out, I may have to drill it later.  Even with the powder coating, the job was only about an hour.

Now, back to the fan.  I determined that the radiator could accept a 16 inch fan nicely, so I went looking for 16 inch fans less than three inches thick.  I also wanted to be careful about the current draw, so that was a consideration, too.  I ended up with a Spal unit.

Spal offers various kinds of plastic mounting tabs that fit into slots on the fan housing, but it looked easier to me to just make something.  The last thing I wanted to do was to mount the fan directly to the core with straps through the fins.  I made four little metal brackets to weld to the radiator frame.  I like my mods on the car to be easily reversible, so I tried to minimize the welds.

One other little job I wanted to do before I painted the radiator was to add a bung for a draincock.  The shop would have done this for no charge, but I forgot to ask them.

Then painted the radiator.  I used a good primer and two coats of high temp paint on the frame and tanks, but since paint won't do anything positive for heat transfer to air, I just dusted the fins with flat black.  The next day, I mounted the fan.

Then there is the small matter of a thermal switch for the fan.  This is often mounted directly on the radiator, but I opted to mount it on the hard pipe between the two lower hoses.  Since my original pipe was pretty rusted and pitted, I ordered a stainless replacement pipe.  Though my expectations are never very high when ordering aftermarket parts, I have to say that in this case, the new part is far superior to the original.

 I mounted the radiator and the pipe and hoses to see where the best place was.  I picked a place low down on the vertical run of the pipe.

On electrical stuff, I try to avoid using the car frame or body (or engine) as a ground return if I can.  I much prefer explicitly wired returns.  Because of this, I hunted down a two terminal, ungrounded switch.  Besides, with a more common single terminal switch, I'd have to figure out a way to ground the coolant pipe.  I made a little brass bung for the switch, silver brazed it to the pipe, then threaded  for the 3/8 pipe thread of the switch.  I'm using a 180 degree thermostat, so I picked a 185 degree fan switch.  My thinking is that there is no point in running the fan until the thermostat is fully open and the temp rises a little more.  This reasoning is a little idealized, though , since the switch point on these switches is usually around +/- 10 degrees, and the thermostat probably isn't any better.  So there might be some tweaking later.

So here are some of the other parts associated with the radiator.  The top hose is actually from an earlier model car since I won't be using the thermostatic vacuum dump normally found on the '74.

The stainless hose clamps are described as "constant tension".  This is accomplished by that stack of Belleville spring washers on the tightening screw.  I don't know how important that is, but my geeky side liked it.  More important to me was that the clamp band extended over the tooth cutouts so that the hose cant extrude through them.

Because the radiator drain is above the belly pan, I wanted a drain cock that I could attach a hose to.  I was surprised to find one where even the turning handle was brass.  Mostly those are plated steel, and they usually rust pretty quickly.

The thermostat housing, new thermostat, homemade gasket (forgot to order one), and replated original hardware.  I was tempted to polish up the housing, but the Stanpart logo and other lettering make it really hard to do a good job.  Besides, in an engine compartment, the shine doesn't last long.  In the end, I powder coated it silver.

So, putting everything together, it's starting to look like transportation.

The spring loaded hose clamps take up a little more room, but can actually be easier to reach and operate.

The fan switch is pretty accessible, but I have to think of a good way to protect the connections from water.

Finally, I mounted a piece of hardboard in front of the radiator to protect the delicate fins.

This was a fun part of the project.  It was fairly expensive, but almost entirely due to the outsourced work.

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