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March 11, 2021

Radiator & Fan

The GT6, like just about all other liquid cooled cars, used a pump-assisted thermosiphon cooling system.  Coolant picks up waste heat from the engine and transports it to the unfortunately named "radiator", where the heat is transferred to the environment.  "Radiator" is a misnomer because radiation doesn't play a large part in the heat transfer.  Convection is the main mechanism to shed heat to the surroundings, and the efficiency of the convection is boosted by actively forcing air through the radiator.  In the stock GT6, the forced convection is accomplished by a crankshaft mounted fan.

While this mechanical fan is dirt simple and pretty effective, it isn't ideal.  First, the fan spins the fastest at high road speeds, when it isn't really needed at all.  At idle, airflow from the fan may be marginal during hot weather.  Further, spinning the fan takes significant work, and this reduces the power available to go to the wheels.  For this reason, I (and many others) decided to investigate an electrically driven fan.  An electric fan can be controlled by a thermostat, so it is only spinning (and using energy) when it is actually needed.

But  first, the radiator itself.  This 52 year old radiator actually looked pretty good, aside from the fact that most of the paint was gone or in bad shape.




The first task was to see if the radiator was water tight.  I wedged in pieces of plastic laminate on each side of the core to protect the fins while I was handling the radiator.  I plugged the bottom outlet, put the radiator in the shop sink, and filled it with water.




Well, it leaked like a sieve.  I couldn't actually see where it as leaking, but it was near the bottom of the core.  This is probably why most of the paint on the bottom tank was gone.

So, with an unusable radiator,  I had to decide what to do about it.  Do I have the original repaired?  Replaced?  If replaced, copper/brass, or aluminum?  Aluminum radiators are relatively cheap and popular, but anecdotes abound about short lifetimes. 

I took the radiator to a local place that specializes in classic car radiators.  They told me that the core wasn't really repairable, but that it could be re-cored.  I ended up having my original radiator re-cored for about the same cost as a quality US made aluminum radiator.

I asked them to not paint the outside of the radiator, since I still had some work to do on it.  A repaired, but unpainted radiator is not exactly a thing of beauty.





The shop paid a lot of attention to detail, like removing minor dents, and replacing these soldered on tags.  I didn't even notice them before.




And for me, one of the reasons to keep the original is details like this.




One thing I had to do before painting is to install a bung for the fan temperature switch.  Two schools of thought place this switch at the top or at the bottom of the system.  I think either can work, possibly with a different temperature spec for the switch.  The bottom switch on my TR6 seems to work just fine, so decided to install the switch in the bottom radiator tank.  The switch I bought was clever, I thought.  The slug in the center screws into a bung in the radiator, and the switch (on the left) screws into the slug.  This way, the switch can be replaced without draining the cooling system.  The piece on the right is a the home made bung.




Installing the bung.




While the radiator was at the shop, I ordered and received this Spal 12-inch puller fan.  It's a perfect fit for this radiator.




The fan has four mounting eyes.  I just needed to make four little brackets.




Started with some little steel tabs, silver brazed in some studs, and then zinc plated them.




Then welded them in place.  They are pretty easily removable  if some future owner doesn't appreciate this mod.




A couple of coats of a two part epoxy primer, followed by a satin top coat made the tanks and frame look a lot better.





Heavyish paint wouldn't do anything to improve heat transfer of the core though, so it just got a dusting of flat black for appearance.




And then the fan went home.




This was not a very difficult project, but a fairly expensive one.  Around $550 for the re-coring and the fan.


Comments to Ed at elhollin1@yahoo.com

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